Favorite and least favorite US- Canada Border Crossings

[J N Winkler]

As to expansiveness of border search, it doesn't really matter whether we agree with the legal doctrine underlying it--it is still what prevails.

The Constitution trumps "international convention" . . .

Not in this case.  The Constitution was deliberately designed to permit pass-through of English common law and certain legal institutions, such as the inviolability of diplomats (which is one reason foreign diplomats in the US can still get away with rape and murder with no sanction stronger than being declared persona non grata and deported) and expansive border search.

The Europeans have no border controls between each other, and those countries hate each other!

The Europeans have a customs union, which is not the same thing at all.  Also, the EU countries have a very high degree of economic, technological, and infrastructural integration, which undercuts surface rivalries.

And as you said, US citizens are guaranteed entry.  That means that any procedures for determining whether one should be allowed to enter should not apply, yet you still have to prove yourself "worthy" of returning home before they'll let you go.

I would not characterize it quite that way.  Entry of your person is the only thing you get by unquestioned right as an US citizen.  Everybody who enters--whether US citizen or alien--has to satisfy the customs officers that he or she is not carrying contraband or dutiable goods which neither fit within duty-free allowances or have had all applicable duties paid.

And yes, I'm in favor of eliminating the border.  If Europe can do it, so can we, at least as long as people can stop being paranoid over "terrorism".  Why does the government always insist on creating a boogeyman so that it can implement wartime policies without question?

We have had strict border inspections for a lot longer than "securing the homeland" has been a policymaker's buzz phrase.  In fact inspections have been much stricter in the past, even in times of peace.  For example, my grandmother took several trips to western Europe in the early 1980's (before the Visa Waiver Program made travel to the US accessible to the masses in the EU-15) and remembered standing in line at Philadelphia International Airport waiting for a customs officer to open her suitcase and inspect the contents.  In contradistinction, I have never had to open my suitcase for a customs officer since I began flying between the US and western Europe in 1998.

In regard to the US-Canadian border, I am not really opposed to the idea of our having a customs union with Canada.  However, the political and legal obstacles to such an union are not all on our side.  It is true that Canada will admit travellers from some groups which we would not want to admit to the US without close inspection, but Canada also doesn't want to give up collecting duty from Canadians returning with US-purchased goods.  An open border would, for example, make a mockery of super-high Canadian cigarette duties, which are imposed for health reasons.

[agentsteel53]

I'd be in favor of South America style border crossings between the US and Canada.  the border would be closed, but the officials would be more cooperative than interrogative.  I'll never forget that in Chile and Argentina, we made (horrors!) friendly small talk with their officers! 

here, one is automatically assumed to be a threat just for wanting to enter the US.  (either a 'dirty foreigner', or in the case of a US citizen, a near-traitor who dared leave the glorious Homeland)  that strikes me as the most absurd part of this whole charade - being treated like a criminal, as opposed to someone who happens to want to cross an international boundary.

[agentsteel53]

(which is one reason foreign diplomats in the US can still get away with rape and murder with no sanction stronger than being declared persona non grata and deported)

is there an expectation, however, that the country to whom the diplomat belongs is expected to take care of the offender? 

I can imagine if a diplomat actually raped and/or murdered someone on US soil, the Secretary of State of Elbonia would be apologizing profusely and releasing video of the former diplomat being thrown into a dingy Elbonian jail.

[Kniwt]

here, one is automatically assumed to be a threat just for wanting to enter the US.  (either a 'dirty foreigner', or in the case of a US citizen, a near-traitor who dared leave the glorious Homeland)

Going slightly off-topic here, but I recently had my most pleasant re-entry ever to the USA, and it was at Los Algodones, B.C. / Andrade, Calif. -- although a lot of that had to do with it being Christmas Day and me being the only -- only! -- pedestrian in the whole inspection office. I had bicycled about 15 miles to Cd. Morelos and back, and there was literally nobody in the entire huge waiting area that was set up for pedestrians.

I walked up to the office, the door was closed, and the officer motioned for me to come in. His first words to me, after looking at my bike, were: "You don't get one of those at Walmart, do you?" We had a chat where all the key points were hit -- where I was from, why I'd done it (because it was Christmas, probably the least-congested day of the year to do it), and we spent about 10 minutes, and all the other idle officers joined in. Nothing was searched, it was just a chat, and not a single other pedestrian came in the whole time. I finally cut the whole thing short by saying that I needed to ride the final couple of miles back to my car before sunset.

Quite unlike the time re-entering at Blaine, Wash., in 2004 when upon hearing that I was a newspaper editor at the time, his next question was: "What do you write about the war?"

[agentsteel53]

Quite unlike the time re-entering at Blaine, Wash., in 2004 when upon hearing that I was a newspaper editor at the time, his next question was: "What do you write about the war?"

I absolutely despise that style of questioning, and am disgusted that it is part of the standard operating procedure for a government office which claims itself to be a legitimate arm of a democratic government.

[english si]

The Europeans have a customs union, which is not the same thing at all.

Though it should be said that Schengen != Common Market - they aren't the same in overlap. Switzerland and the Common Market have a relationship similar to that of the US and Canada, but Switzerland is in Schengen (and the Common Travel Area isn't, but is mostly in the Common Market).

And while the customs union exist, bodies like HMRC can stop you bringing too many things that come under 'vice taxes'. French lower vice taxes spawned the 'booze cruise' trend, going to Warehouse booze-and-biscuits places in Calais for the day and filling your boot full of vice products, coming back. The question is 'personal use only', much like the Duty Free (which I remember existing for inside EU-15 travel via boat or plane - not the case now), but with higher limits as you did pay duty.

Then again, Switzerland is small, has several major transit routes between the surrounding countries, a wiggly border and such like. The irony is that they fairly recently spent a lot of money at Euro-Airport and Geneva Airport on separate Swiss/Schengen border controls (I'm pretty sure they did them up not too long ago). I guess it's still needed for the customs though.

[J N Winkler]

And while the customs union exists, bodies like HMRC can stop you bringing too many things that come under 'vice taxes'. French lower vice taxes spawned the 'booze cruise' trend, going to Warehouse booze-and-cigarettes places in Calais for the day and filling your boot full of vice products, coming back. The question is 'personal use only', much like the Duty Free (which I remember existing for inside EU-15 travel via boat or plane - not the case now), but with higher limits as you did pay duty.

I remember reading the court decision in the Hoverspeed case, where a group of friends drove an Escort down to France from Lancashire, and were caught on the return journey trying to bring in an unbelievable amount of alcohol and tobacco from France.  They tried, unsuccessfully, to claim that it was exempt from duty on the basis that they collectively were a private members' club and the booze and baccy had been purchased for their sole use.

It is also true that the EU member states are aware of the possibility of VAT fraud even for merchandise that does not fit the traditional vice categories.

So, a customs union does not preclude revenue enforcement even under the relatively liberal terms under which it is run in the EU.  For Canada (my impression has always been that Americans are nowhere near as keen as Canadians to collect duty from tourist travellers), I suspect the added cost and customer burden of tight inspections are deemed worth it for the added certainty of revenue collection and interdiction of vice merchandise which would otherwise cross the border in commercial quantities.

[vdeane]

Not in this case.  The Constitution was deliberately designed to permit pass-through of English common law and certain legal institutions, such as the inviolability of diplomats (which is one reason foreign diplomats in the US can still get away with rape and murder with no sanction stronger than being declared persona non grata and deported) and expansive border search.

Where in the document does it say anything like that?  I don't care one bit for anything the supreme court says - if the supreme court says something that the actual text of the document doesn't say, then the supreme court is wrong as far as I'm concerned.

We have had strict border inspections for a lot longer than "securing the homeland" has been a policymaker's buzz phrase.  In fact inspections have been much stricter in the past, even in times of peace.  For example, my grandmother took several trips to western Europe in the early 1980's (before the Visa Waiver Program made travel to the US accessible to the masses in the EU-15) and remembered standing in line at Philadelphia International Airport waiting for a customs officer to open her suitcase and inspect the contents.  In contradistinction, I have never had to open my suitcase for a customs officer since I began flying between the US and western Europe in 1998.

In regard to the US-Canadian border, I am not really opposed to the idea of our having a customs union with Canada.  However, the political and legal obstacles to such an union are not all on our side.  It is true that Canada will admit travellers from some groups which we would not want to admit to the US without close inspection, but Canada also doesn't want to give up collecting duty from Canadians returning with US-purchased goods.  An open border would, for example, make a mockery of super-high Canadian cigarette duties, which are imposed for health reasons.

I've only been across the land border with Canada, so I wouldn't know anything about air travel or Mexico, but before 9/11 going through customs was no more of a burden than taking your toll ticket to enter the Thruway.  My, how things have changed since then...  In many places the border was a mere formality.  In some places, it didn't even exist for all practical purposes (such as Derby Lane, VT and Stanstead, QC, which had no customs controls if you avoided US 5 and I-91, and nobody cared; this also held for the 1000 Islands on boat prior to the post-9/11 construction of the customs booth at Boldt Castle).

I remember that during the 90s the US and Canada were actively working towards eliminating the border, so I'm not sure what changed other than 9/11.  I have noticed that Canadians are less lenient on duties, probably because 90% of their population lives within driving distance of the US, while the majority of the US population would have to drive far away to get to Canada.

My biggest beef with the border is that it's inconvenient for roadgeeking.  I've done several road trips in the US where I had no other purpose whatsoever than to clinch highways (though my winter ones are allegedly to "keep the car running").  Any foray into Canada needs at least some other purpose, so it naturally follows that my clinched mileage in Canada is much lower than in the US despite having lived within 40 miles of the border my entire life (well, except for one summer internship, that is).

I've also gotten the "why would you go to Canada when we have everything in the US" attitude from customs at least once.

[J N Winkler]

Not in this case.  The Constitution was deliberately designed to permit pass-through of English common law and certain legal institutions, such as the inviolability of diplomats (which is one reason foreign diplomats in the US can still get away with rape and murder with no sanction stronger than being declared persona non grata and deported) and expansive border search.

Where in the document does it say anything like that?  I don't care one bit for anything the supreme court says - if the supreme court says something that the actual text of the document doesn't say, then the supreme court is wrong as far as I'm concerned.

The Constitution doesn't say anything directly--it merely leaves existing law untouched.  That is how written constitutions typically work.  Most states have overhauled their state constitutions several times but in each case the existing body of law has been carried through from the old constitution to the new one (except in isolated cases where legal provisions which have become unconstitutional are either repealed or allowed to stand without enforcement).

(To answer Jake's question upthread:  I am not aware that the home country is expected to try diplomats accused of serious crimes in the countries to which they are accredited.  I think the more usual procedure is for the diplomat's home country to waive immunity so that the diplomat can be tried in the country where the crimes occurred, but the greasier the villain, the less likely this is to happen.)

I've only been across the land border with Canada, so I wouldn't know anything about air travel or Mexico, but before 9/11 going through customs was no more of a burden than taking your toll ticket to enter the Thruway.  My, how things have changed since then...

Has it, really?  The only change which I have actually experienced at the land border is the need to use a passport because of WHTI.  Even in 1991 we had to do a verbal declaration when re-entering the US from Canada, so it was not as casual as picking up a Thruway toll ticket.

In many places the border was a mere formality.  In some places, it didn't even exist for all practical purposes (such as Derby Lane, VT and Stanstead, QC, which had no customs controls if you avoided US 5 and I-91, and nobody cared; this also held for the 1000 Islands on boat prior to the post-9/11 construction of the customs booth at Boldt Castle).

These have seen considerable change since 9/11, I will grant you that, but I think they qualify as edge cases.

I remember that during the 90s the US and Canada were actively working towards eliminating the border, so I'm not sure what changed other than 9/11.  I have noticed that Canadians are less lenient on duties, probably because 90% of their population lives within driving distance of the US, while the majority of the US population would have to drive far away to get to Canada.

There was a lot going on in the mid-1990's besides it being before 9/11.  NAFTA had just come into effect, so there was a lot of policy momentum in favor of cross-border integration.  Several commentators, notably Lester Thurow, floated the idea of the NAFTA area turning into a sort of clone of the EU, with a customs and immigration union between the US and Canada at the least, and supernational institutions coordinating key areas of trade and economic policy.  At this time the EU seemed to have the potential to be more competitive economically than the US because it represented a potential unified economic and common-currency area with a population greater than that of the US, a per capita income comparable to that of the US, and full internal mobility of capital and labor comparable to that prevailing in the US.  It really did look at the time as if the US would need to enter into a much closer partnership with its neighbors in order to compete in a new managed-trade world consisting of multi-country blocs such as the EU, MERCOSUR, SADC, etc.

The problems the EU has had economically since the early noughties have taken away a lot of momentum for cross-border integration in the NAFTA zone.  The euro has been the next best thing to a failure, because there is not enough labor mobility in the euro area to offset the disadvantages of the uniform interest rate.  The eurozone has turned out to be much smaller than envisioned in the 1990's because several big players in the EU, notably Britain and Sweden, steered clear of the single currency after first intimating that they might join.  The EU as a whole is aging, and not bringing in enough new blood through immigration to stave off crises in old-age pensions and other social provision.  No cure is in sight because EU immigration policy is overtight and sclerotic, and the agenda is owned by right-wing parties which resist expanded immigration.  We in the US no longer worry about a resurgent EU; instead we fear an EU collapse.

Put simply, a lot of the impetus for customs and immigration union with Canada that existed in the 1990's is just not there anymore.

My biggest beef with the border is that it's inconvenient for roadgeeking.  I've done several road trips in the US where I had no other purpose whatsoever than to clinch highways (though my winter ones are allegedly to "keep the car running").  Any foray into Canada needs at least some other purpose, so it naturally follows that my clinched mileage in Canada is much lower than in the US despite having lived within 40 miles of the border my entire life (well, except for one summer internship, that is).

In my experience, it does not take much of an excuse to get into Canada.

I've also gotten the "why would you go to Canada when we have everything in the US" attitude from customs at least once.

I have never had that reaction.  I have heard "the US has a lot of stuff to see, so why don't you see that first before you travel abroad" staple from my relatives in the US, but never from US customs or immigration officers.  (I think that sentiment originates from a Will Rogers quote, and while I think it is fine to suggest seeing stuff in the US as far as that goes, my outlook is basically internationalist and cosmopolitan, so I don't really buy the idea that the US stuff should be seen first, or that seeing it should be a greater priority than seeing stuff abroad, etc.)

There is a flip answer to that question that can be given--"The US has a lot of stuff to see, but it doesn't have the stuff that is in Canada"--but personally I don't see a need for a conversation with a border official to get onto that track.  The border is no place to get gabby.

[cpzilliacus]

I remember that during the 90s the US and Canada were actively working towards eliminating the border, so I'm not sure what changed other than 9/11.  I have noticed that Canadians are less lenient on duties, probably because 90% of their population lives within driving distance of the US, while the majority of the US population would have to drive far away to get to Canada.

In a perfect world, the United States and Canada would just join the Schengen agreement (and encourage the UK to do the same) and scrap most border controls between the U.S. and Canada.

[Dr Frankenstein]

I have to agree with deanej on the pre 9/11 land borders, especially on rural crossings. At times, we'd get waved through into the US after two questions, and would come back with a simple "Not bringing anything back? - No." without anyone checking any document. The guy was literally yelling away from the door of his office.

[vdeane]

The Constitution doesn't say anything directly--it merely leaves existing law untouched.  That is how written constitutions typically work.  Most states have overhauled their state constitutions several times but in each case the existing body of law has been carried through from the old constitution to the new one (except in isolated cases where legal provisions which have become unconstitutional are either repealed or allowed to stand without enforcement).

The version of history I learned says that the Constitution is the supreme law of the land and that the federal government is not allowed to do anything not explicitly stated in the Constitution.  It is this interpretation that I follow.

Has it, really?  The only change which I have actually experienced at the land border is the need to use a passport because of WHTI.  Even in 1991 we had to do a verbal declaration when re-entering the US from Canada, so it was not as casual as picking up a Thruway toll ticket.

From what I remember, in the 90s a typical customs stop with my family on I-81 would consist of "where are you from", "where are you going", and "welcome to Ontario" (note that these days they always say "you're all set" if they say anything at all when handing back documents; I guess this was too friendly).  I didn't even realize that countries were more different from each other than states were until I was in middle school or high school, and I still didn't think of Canada as "foreign" until WHTI.  I've also noticed that the amount of places in the 1000 Islands flying both US and Canadian flags has gone down significantly in the past two years.

These have seen considerable change since 9/11, I will grant you that, but I think they qualify as edge cases.

I never have, but then again I can count on two fingers the number of times I've crossed outside the St. Lawrence, and both of those were at Niagara Falls.

In my experience, it does not take much of an excuse to get into Canada.

True, but most of my trips consist of "drive for 8 hours stopping only for food and gas".  At some point I hope to get some trips that consist of more than food and gas for Canada, but it's dependent on me getting a job right now.

The border is no place to get gabby.

Sometimes the officials don't leave a choice, though I don't usually get that problem now that I have my enhanced driver's licence for some reason.

[kphoger]

I have to agree with deanej on the pre 9/11 land borders, especially on rural crossings. At times, we'd get waved through into the US after two questions, and would come back with a simple "Not bringing anything back? - No." without anyone checking any document. The guy was literally yelling away from the door of his office.

As recently as three years ago, I was waiting in line at the CBP exit checkpoint leading to the Colombia border crossing (upriver of Laredo), when a pickup just drove up alongside the queue of vehicles.  He stopped next to our car, which was at the head of the line, and rolled down the window.  One CBP official shouted to the other one, "Frequent crosser", and they waved the guy on without further ado.  Of course, that was southbound; I don't know if they do the same thing northbound.

[agentsteel53]

seems like an exit interview is much more at the discretion of the CBP officers present.  I doubt that they would have that kind of informal "Sentri line" for inbound traffic.

[english si]

In a perfect world, the United States and Canada would just join the Schengen agreement (and encourage the UK to do the same) and scrap most border controls between the U.S. and Canada.

If the US joins, then we would join in a snip.

Our current problem with Schengen is
1)Countries out east don't really want to enforce the border that much - partially as they will just be a transit country for immigrants
2)Most of the illegal immigrants want to go to the UK, where there's little room for them - even those who love immigrants agree about the lack of space
3)Our not being in Schengen means that we can deal with those who illegally want to get here, rather than relying on an Eastern European country - working with the French authorities, we sorted out the camps of people trying to cross the channel for instance (it was a major embarrassment for the French that they had a load of immigrants living there in tents trying to leave them for England)

If the US joins Schengen then its money for strict border controls will exist on that eastern frontier and there'd be a country (well 2) with space, more jobs, etc - instead of aiming to cross the Channel, they'd be aiming to cross the Atlantic.

The moment, however, you lecture us about integration with our European friends, you've just turned a large number of people against that aim - either by being evil America, or by reminding us of those glorious British freedoms and ideals we once had and the process that caused us to (first of all) lose you guys and finally end up yoked to these people who just don't get those long-lost ideals (and even despise such ideals).

[DBrim]

* Fort Kent, for its beauty

I didn't like Fort Kent because the US Guards simply could not comprehend me wanting to take ME-11 over 1 or TC2, and thus were very perplexed that I would choose to cross there over the crossing in Edmundston or Houlton.  Over an hour of questioning because of it.

Other least favorites include crossing into Canada along the Alaska highway, since they made us stand outside during winter while they checked our car.  US-bound at Jackman, ME was pretty bad, too.

As Jake already mentioned, the Chile to Argentina crossings were particularly easy and bordered on fun at times.  Except the crossing at Chile Chico, since they close early for no reason and cost us a few hours of good light.

I've never received a US passport stamp when enterring the country via air or via car.

[agentsteel53]

I've never received a US passport stamp when enterring the country via air or via car.

must be different rules for US citizens.  for me (Hungarian citizen, US green card), it's a consistent "yes by air, no by ground".

[vdeane]

Honestly, I've never understood the point of an exit interview.  What's the point of going through customs to leave a country?

[kkt]

Worst experiences:  I was about 8 years old and my grandparents brought me to Baja for spring break along with their younger kids.  My mom wrote a permission letter, but my dad didn't sign it as well.  So the Mexico border guards kept us in the border station for a couple of hours while they got my dad on the phone.  They did let us in after that.  Fair enough, they were just doing their job I guess.  They were polite about it.

More recently, about 2000, we brought a friend from Vancouver to Seattle to visit for a couple of days.  He was a polite, softspoken young man, but for some reason the U.S. border guard saw the need to get an inch from his face and yell.  He was in the Canadian military and showed his military ID when the border guard asked his job.  The guard didn't delay us or have us searched, but I felt ashamed to be American after that treatment.  Friend thought later that reaction was because his ID said "reserve", which in the U.S. means part-time service, but in Canada can mean full-time work but not eligible to be sent overseas.

[realjd]

Honestly, I've never understood the point of an exit interview.  What's the point of going through customs to leave a country?

One of the big reasons is export duties or expert restrictions. It's illegal to export antiquities from many countries for instance, and at the Mexican border the US CBP officers are often looking for undeclared cash leaving the country (anything over $10k must be declared). Other countries charge an exit tax be paid or an exit visa and they're checking for that, and some countries check to make sure the person doesn't have any outstanding warrants or something. It also provides a convenient way for a traveler to get a carnet signed which can be a complete PIA here in the states since you often have to go find some obscure hard-to-find customs office to get that done.

[J N Winkler]

The Constitution doesn't say anything directly--it merely leaves existing law untouched.  That is how written constitutions typically work.  Most states have overhauled their state constitutions several times but in each case the existing body of law has been carried through from the old constitution to the new one (except in isolated cases where legal provisions which have become unconstitutional are either repealed or allowed to stand without enforcement).

The version of history I learned says that the Constitution is the supreme law of the land and that the federal government is not allowed to do anything not explicitly stated in the Constitution.  It is this interpretation that I follow.

The point I think you are missing is that, since the Constitution does not explicitly disallow warrantless border search, and Congress has not specifically banned it, courts are influenced by prior law and judicial precedent in interpreting the Fourth Amendment in respect of border searches.  The legal convention (which pre-dates the Constitution and is considered to have been saved by it) is that customs officers have almost unlimited powers of search, so long as the search happens at the border or is in some other way intimately tied to the act of crossing the border.

[1995hoo]

Honestly, I've never understood the point of an exit interview.  What's the point of going through customs to leave a country?

Some countries with strict access control are very picky about it–in Russia, for example, if you overstay beyond your visa's expiry, you will be fined and you won't be allowed to leave the country until you get your visa extended. Over the years it's frequently tripped up tourists trying to leave on the train from St. Petersburg to Helsinki–the train leaves St. Petersburg in the evening but crosses the border after midnight, so if your visa expires on the day the train leaves, you'll overstay your visa.

As a general matter in the United States, the lack of exit controls is one reason why your duty-free purchases at the airport are delivered to you at the gate when you board the plane. It's how they make sure the tax-free purchases leave the country.

I've never seen exit inspections when leaving the United States except for commercial vehicles, although I see from the comments in this thread that it happens. I've never driven to Mexico, though. Usually when I've crossed the border at major checkpoints there's an exit for "Export Control" and the only people who head over there are commercial drivers. For the majority of tourists it's not much of an issue, although no doubt you've encountered software packages whose labels say there are limits on export (usually due to encryption or some such thing) and so in theory (though usually not in practice) those could pose an issue.

[vdeane]

The Constitution doesn't say anything directly--it merely leaves existing law untouched.  That is how written constitutions typically work.  Most states have overhauled their state constitutions several times but in each case the existing body of law has been carried through from the old constitution to the new one (except in isolated cases where legal provisions which have become unconstitutional are either repealed or allowed to stand without enforcement).

The version of history I learned says that the Constitution is the supreme law of the land and that the federal government is not allowed to do anything not explicitly stated in the Constitution.  It is this interpretation that I follow.

The point I think you are missing is that, since the Constitution does not explicitly disallow warrantless border search, and Congress has not specifically banned it, courts are influenced by prior law and judicial precedent in interpreting the Fourth Amendment in respect of border searches.  The legal convention (which pre-dates the Constitution and is considered to have been saved by it) is that customs officers have almost unlimited powers of search, so long as the search happens at the border or is in some other way intimately tied to the act of crossing the border.

The Constitution doesn't explicitly allow for it either, though.  In case you haven't noticed, I'm a strict constructionist.  As far as I'm concerned, courts shouldn't be allowed to consider anything other than the actual text of the law - not even prior court rulings.

[agentsteel53]

Honestly, I've never understood the point of an exit interview.  What's the point of going through customs to leave a country?

for a country where one has to cancel out their temporary legal stay (visa, etc), it makes perfect sense.  I don't know if this is the case with the US, as I have a much different legal status.  (there is also the shade of difference between a voluntary exit procedure - you yourself pulling over and taking care of your paperwork - versus a mandatory stop.)

for a country whose neighbor does not do consistent entry interviews, it also makes sense.  you can go very far in Mexico without running into a formal aduana checkpoint (all the way down Baja, and ~30km into the mainland) and therefore if guns, large quantities of money, etc, are going into Mexico and about to disappear in the borderlands, the US might as well see if they can put a stop to it. 

edit: everyone else did a better job explaining it!

[kkt]

The version of history I learned says that the Constitution is the supreme law of the land and that the federal government is not allowed to do anything not explicitly stated in the Constitution.  It is this interpretation that I follow.

Stopping people at the border and possibly searching them is allowed under the constitution, if you read it with understanding.  Look at Article I, Section 8, the first and the last paragraphs:

The Congress shall have Power To lay and collect Taxes, Duties, Imposts and Excises, to pay the Debts and provide for the common Defence and general Welfare of the United States; but all Duties, Imposts and Excises shall be uniform throughout the United States;

To make all Laws which shall be necessary and proper for carrying into Execution the foregoing Powers, and all other Powers vested by this Constitution in the Government of the United States, or in any Department or Officer thereof.

In order to collect duties on imports, and for those taxes not to be just a gentle suggestion, they have to be able to search people entering the country; laws and executive orders allowing those searches are necessary and proper.

This is not after the fact justification.  We tried running the country without a "necessary and proper" clause and a shorter list of federal powers.  It was the articles of confederation, and it didn't work very well.  The founders knew they were expanding federal powers when they adopted the present constitution, and meant to do so.