They see the writing on the wall. All four of these Senators are up for reelection next year in states that generally trend Republican. They watched 63 of their colleagues in the House and a few in the Senate get swept out of office just a few months ago in part due to the passage of ObamaCare. Over half the states are suing to have it struck down as unconstitutional and two judges so far agree with them. Angst among the public has really not gone away. Looks like this legislation wasn't so "historical" after all.