Pryor is facing a tough reelection battle in the heavily Republican state, and President Obama and his signature law are deeply unpopular in Arkansas. Republicans have already been ripping Pryor for his vote in favor of the Affordable Care Act, though he hasn't shied away from questions on his vote.

Clinton still has high popularity in his home state. Pryor was happy to have the president host a $1 million fundraiser for his reelection campaign earlier this year, and Arkansas Democrats are hopeful the Clintons can help boost them in 2014. But Pryor seems to have calculated that tying himself to Clinton wasn't worth further tying himself to the unpopular law this time around.

This post was updated at 12:40 p.m.