Mike makes some good points about the risks facing Democrats now that Republicans are saying, "You guys have the votes, pass a bailout bill on your own if you're so worried about it."
But I don't think it's that tricky to respond. Can't Pelosi always just come back and say, "No, actually we don't have the votes. We really need some help from our Republican colleagues." For one thing, who's going to prove her wrong? Is some Republican going to take an independent whip count? A media organization? Even if that were possible, these numbers are so fluid they can change right up until the moment of a vote.
Second, when has an appeal for bipartisan support ever been a political loser? Doesn't the side that rejects such an appeal generally look petty and self-interested? If Pelosi were to say, "There's a chance we could ram this down their throats, but it's too important to turn into a partisan issue," who would say she's the bad guy?
The GOP clearly wants the best of both worlds here--a bill that ends the financial crisis, but without their fingerprints on it, so they can turn around and bash Democrats. But I don't see what's in it for the Dems. If you look at the polls out this week (see here and here, for example), the financial crisis makes Democrats look more, not less, appealing in the eyes of voters. So it's the GOP that's under more pressure to pass something. (Though I agree that there could be a huge conservative backlash if the GOP is involved--that's the circle they have to square.)
Bottom line: I don't find the GOP threats very credible.
P.S. It looks like the House Dems are holding a press conference at 4:30, so stay tuned.