They have lost a lot of support and will probably lose quite a few seats in 2010 - if the economy continues to lag obviously that would also factor into any losses, but their complete indifference if not outright hostility to the majority's opinion on this bill will be a big factor.
They seem to have made a long term calculation that once they get millions of people on it, the tide will turn, even if the results are pretty awful - on the budget, increased waiting times for certain treatments, increased premiums, higher taxes etc. From that point they can tell everyone that's on it that the Repubs want to get rid of it, and then they'll have nothing. Think about it - that's been a recurring theme for decades on social security and medicare - at least alleged cuts if not elimination. Kerry announced on the eve of the 2004 election that Bush had a "secret plan" to cut social security (and reestablish the draft) right after the election.