Democrats may have scored a big victory on the first Senate health care overhaul vote, but party unity lasted only as long as it took to bring down the gavel on Saturday's vote.
Sixty senators -- exactly the number needed to pass a bill -- voted Saturday night to move forward with debate. But even as they voted yes on this first procedural votes, several Democrats warned they'll vote no on the next vote if the bill isn't changed.
"I'm prepared to vote against moving to the next stage of consideration as long as a government-run public option is included," said Sen. Blanche Lincoln, D-Neb., who has been a swing Democratic vote on the Senate's bill.
She's one of four Democrats who voted "yes" on bringing the bill to the floor for debate -- but who say they'll vote "no" next time if the bill still includes a government-run insurance program.
Since no Republicans support the bill, losing four Democratic votes would mean the bill only has 56 "yes" votes -- not enough to pass.
A House DividedSenate Majority Leader Harry Reid, D-Nev., could try to win support by taking the public option out, but that move is also problematic.
There are at least two Democrats who say they'll vote against any bill that does not include a public option, and there may be many more.
"I'll vote against any bill without a public option," said Sen. Roland Burris, D-Ill.
"I don't want four Democratic senators dictating to the other 56 of us and to the country," said Sen. Sherrod Brown, D-Ohio.
That leaves Majority Leader Reid in a bind. If he keeps the public option in the bill, he may lose four votes. If he takes the public option out, he could lose at least two votes.
Either way, the bill would go down because Reid can't afford to lose a single vote.
Health Care: Reid in a Bind as Dems Take a Stand
Democratic leaders could try to convince two or more Republicans to support their bill. Sen. Olympia Snowe, R-Maine, has said she'd support a so-called "trigger," which would create a public option several years from now only if there isn't enough competition among private insurance companies.
Such a compromise could work in the Senate, but many House Democrats have been cold to the idea of a trigger.
House Speaker Nancy Pelosi, D-Calif., has said she won't even talk about the possibility. "A trigger is an excuse for not doing anything," she said.
Even if Democrats find a way to get a compromise on "the public option," their differences over health coverage for abortion and illegal immigrants may prove even more difficult to resolve.
So many Democrats have drawn so many lines in the sand on what they can and can't support that the only way anything may get passed is if several of them go back on their word.
ABC News' Devin Dwyer contributed to this report.