Obamacare is the Atomic bomb to the Republicans. They know people will like it and they are worried that will be reflected in the voting booth.
This is just a repeat of history:
December 2,
1993 - Leading
conservative operative William Kristol privately circulates a strategy
document to Republicans in Congress. Kristol writes that congressional
Republicans should work to "kill" -- not amend -- the Clinton plan because it
presents a real danger to the Republican future: Its passage will give the
Democrats a lock on the crucial middle-class vote and revive the reputation of
the party.
http://www.pbs.org/newshour/forum/may96/background/health_debate_page2.html