On November 8th, when the House narrowly voted to approve the Democrats' health care bill, voters opposed the measure by about a 49-42 margin, according to the Pollster.com trendline. Right now, the numbers are -- well, almost exactly the same: 50.2-42.5 against if you want to be precise:
This is not to suggest that a House member who voted for health care in November wouldn't have some reasons to oppose the bill now. For one thing, the Democrats' position in the generic ballot has declined somewhat (although President Obama's approval rating really hasn't). For another, we're now a few months closer to the midterms.
Still, what's probably changed the most is the attitude of the Democratic caucus in the wake of Scott Brown's victory in Massachusetts along with several prominent retirements among Democratic Congressmembers. It's not that the forecast has really changed all that much since November -- although clearly the Democrats have lost some further ground, especially because of their Senate-side retirements -- as that its consequences have become more manifest.