Some Democratic senators say they'll jump ship from the bill without tighter restrictions on abortion coverage. Others say they'll go unless a government plan to compete with private insurance companies gets tossed overboard. Such concessions would enrage liberals, the heart and soul of the party.
There's no clear course for Senate Majority Leader Harry Reid, D-Nev., to steer legislation through Congress to President Barack Obama. You can't make history unless you reach 60 votes, and don't count on Republicans helping him.
But Reid is determined to avoid being remembered as another Democrat who tried and failed to make health care access for the middle class a part of America's social safety net.
"Generation after generation has called on us to fix this broken system," he said at a recent Capitol Hill rally. "We're now closer than ever to getting it done."
His bill includes $848 billion over 10 years to gradually expand coverage to most of those now uninsured. It would ban onerous insurance industry practices such as denying coverage or charging higher premiums because of someone's poor health. Those who now have the hardest time getting coverage - the self-employed and small businesses - could buy a policy in a new insurance market, with government subsidies for many. Older people would get better prescription coverage.
Most people covered by big employers would gain more protections without major changes. One exception would be those with high-cost insurance plans, whose premiums could rise as a result of a tax on insurers issue the coverage.
The public is ambivalent about the Democrats' legislation. While 58 percent want elected officials to tackle health care now, about half of those supporters say they don't like what they're hearing about the plans, according to a new Kaiser Family Foundation poll.
The Senate debate risks alienating more people because much of the discussion probably will revolve around divisive issues that preoccupy lawmakers.
"A large portion of the debate will be spent on issues that aren't important to the workability of health reform," said Paul Ginsburg, president of the Center for Studying Health System Change.
The debate should start off modestly, with each side offering one amendment. No votes are scheduled Monday.
But with more than 40 senators on the two committees that originated the bill, many more amendments are expected. Some likely subjects are limits on malpractice lawsuits, consumer choice, affordability, minority health and drug prices.
Reid wants to finish by Christmas; he may not get to.
He's hoping that Democrats will stick together on procedural matters, where Senate rules require 60 votes to advance. That would allow for different views to be heard on the underlying questions. But such an accommodation might not always be possible.
For example, the National Right to Life to Committee says unless there are big changes, it will count the procedural motion to allow a final up-or-down vote on the legislation as tantamount to a vote on abortion.
Of the many issues senators have to weigh, abortion funding and the option of a government insurance plan promise to be the most difficult.
On abortion, no compromise seems possible. On the public plan, a deal may yet be had.
The House adopted strict limits on abortion funding as the price for the support of anti-abortion Democrats. Abortion rights supporters are now backing Reid's approach, which tries to preserve coverage for abortion while stipulating that federal dollars may not be used except in cases of rape, incest or to save the life of the mother. Catholic bishops say they can't accept that because it would let federally subsidized plans cover abortion.
It might be easier to find a middle ground on the issue of a public health plan to compete against private insurers.
Reid's bill would create a national plan, but give states the choice of opting out. In any event, the Congressional Budget Office now estimates that the government would not be the bare-knuckles competitor insurers had feared, but a relatively minor player in the market.
Several moderate Democrats have served notice they can't support Reid's approach. The lone Republican to vote for the Senate bill in committee, Olympia Snowe of Maine, has said she could accept a public plan if insurers are given one last chance to deliver lower premiums in a competitive market. Combining Snowe's "trigger" with Reid's "opt-out" might be the answer.
If that's the case, it still would have to pass a final test: 60 votes.