Is US 159 the shortest US highway to enter 3 states?

[bugo]

NE2?

[usends]

Yes: there are 14 US routes shorter than US 159, and none of them go through 3 states. 
Historically, there have been an additional 25 routes shorter than 159, but again, none of them went through more than 2 states.

[hotdogPi]

What about US 44 for 4 states?

[agentsteel53]

the longest US highway which is only in two states appears to be 277: 632 miles in Oklahoma and Texas. 

someone can prove me wrong.

[usends]

the longest US highway which is only in two states appears to be 277: 632 miles in Oklahoma and Texas. 
someone can prove me wrong.

I probably would've believed you, except you added that last sentence, so I had to look. 
Found a couple that are longer:
US 380: 677 miles in NM and TX.
US 190: 875 miles in TX and LA.

[Alps]

US 730 is the shortest US highway to enter 2 states.

[bugo]

US 277 could (and should) easily be extended to US 60 or US 64 along OK 74.

[usends]

US 730 is the shortest US highway to enter 2 states.

Also interesting to note here that the shortest mainline US route ever (US 630, at just under 3 miles) served two states.  (But that designation was retired in the '30s.)