Getting health-care reform to this point has been like a game of chess, a test of strategic skill, with each move prompting a countermove as the surviving elements of the bills progress through the process. It's a major accomplishment for President Obama and the Democrats to have gotten this far, but now the game changes. From here on, passing legislation is more like a game of dominoes than chess, with lawmakers who fall into line taking their neighbors down with them. (Click here to follow Eleanor Clift)

Talking with one of the pro-reform lobbyists on health care, I learned to my surprise that Connecticut Sen. Joe Lieberman is a crucial swing vote. If he turns against it, he may take others with him. He's not on either of the Senate committees that wrote the bills being considered, and he's just one vote. But if you can't get Lieberman, an independent Democrat, to vote for health-care reform, you're unlikely to get conservative, red-state Democrats like Evan Bayh of Indiana and Ben Nelson of Nebraska to back it, since they'll be reluctant to be seen as to the left of Joe Lieberman.

Lieberman caught some flak from Democrats this week for declaring on the Don Imus show that he opposes the Baucus bill in its current form. He's been echoing Republican criticism for some time that Obama is trying to do too much and that health-care reform should be done piecemeal. Insurance industry warnings that premiums will rise under the Baucus plan gave Lieberman more ammunition.

Then again, the insurance industry report backfired when advocates of a public option used it to bolster their case that without it, there's no brake on rising premiums. Liberal senators like New York's Chuck Schumer and West Virginia's Jay Rockefeller are fighting hard for a public option, but they're dismissed as the usual suspects. They don't carry anywhere near the under-the-radar clout of Lieberman or the outsized influence of Olympia Snowe, the only Republican on the Senate Finance Committee who voted for the Baucus bill.

Lieberman is opposed to a public option, saying it's a nonstarter for him. My pro-reform health-care lobbyist tells me that if Democrats make the public option essential to passage of reform, the whole thing will implode. When she starts counting votes to see how the Democrats could reach the 60-vote threshold in the Senate needed to avoid a Republican filibuster, she figures they could probably get Lieberman to accept a trigger, meaning that if the insurance companies don't live up to their promises to lower costs and keep premiums reasonable, a government option would automatically kick in after three to five years. She calls it a "sword of Damocles over the industry that they need to do the right thing, because they won't do it on their own."

Snowe is the trigger lady. It's her idea, and the Democrats will have her support only if they have the trigger. She would bring along Lieberman. And if the guy who feels most at home hanging around with John McCain, Lindsey Graham, and Susan Collins can vote for health-care reform on the Senate floor, that gives a sign to centrist Democrats to fall in line. Lieberman considers himself an economic centrist, a foreign-policy hawk, and a social liberal, which means that he usually votes with Democrats on domestic policy.