More than nearly any other issue, abortion has the potential to throw a wrench into the already fragile gears of the major health care overhaul now starting to churn on Capitol Hill.
"I take a view that there's almost anything [that can be compromised] in public affairs except probably the issue of abortion," said Sen. Charles Grassley (R-IA), one of the leading Republicans seeking a bipartisan health bill.
Already in the House, 19 Democrats have written House Speaker Nancy Pelosi vowing not to vote for any health bill that includes abortion funding.
"We cannot support any health care reform proposal unless it explicitly excludes abortion from the scope of any government-defined or subsidized health insurance plan," said the letter, whose lead signers included Dan Boren of Oklahoma, Bart Stupak of Michigan and Minnesota's Collin Peterson.
On Monday, the Senate Committee on Health, Education, Labor and Pensions, the only one of five congressional committees overseeing the health effort that is actually drafting its bill, debated a half-dozen abortion-related amendments. It defeated most on identical 12-11 votes, including one that would have barred people who get government insurance subsidies from buying private insurance plans that include abortion coverage.
Sen. Tom Coburn (R-OK) said the principle is the same as the one that currently bans funding for abortion in the Medicaid program for the poor.
"You are taking federal tax dollars and using them to provide abortion services," he said. "The rest of the people in this country should not be paying for [those] services through their tax dollars."
But Sen. Sheldon Whitehouse (D-RI) said that not letting people use what might be very small subsidies to buy private coverage was going too far.
"The next step in this logic will be to require anybody seeking these services to walk to the clinic, lest they use federal highways, supported by federal highway funds," he said.
The committee's debate was relatively brief, but the abortion issue hangs over the health overhaul effort like a dark, menacing cloud.
Abortion foes, like Douglas Johnson of the National Right to Life Committee, say President Obama and congressional leaders plan to use the health care effort to dramatically increase the availability of abortion services.
"These bills give federal officials the authority to define what benefits must be carried in all health insurance plans, both private and in the government plan that's proposed," he said. "And there is no doubt whatever that abortion, elective abortion, would be among those services mandated."
Johnson says that extending existing government abortion funding bans to people who get government subsidies to buy private insurance is a logical extension of a long-standing — and long-settled — policy.
"There has been a consensus at the congressional level since the mid-1970s that taxpayer funds should not be used to pay for elective abortion, and that's simply the principle that we seek to preserve here," he said.
And it's not just government-run plans that bar abortion, he notes. It's government-subsidized plans, too. The program that covers federal workers and their families — as well as members of Congress — he said, "is a program that involves hundreds of private insurance plans, but in order to participate in the program, by act of Congress, the plans may not cover abortion, except to save the life of the mother, or in cases of rape and incest. So elective abortions are not covered under that program because it is federally subsidized."
But Democratic pollster Mark Mellman said such a restriction may not go over so well with the public.
"Right now, most health care plans cover abortion, cover contraception, cover women's reproductive health," he said. "To some extent, what they're talking about on Capitol Hill is taking away coverage that people already have. Americans want health care reform. But they will oppose health care reform if it takes away the coverage they now have for things like abortion and contraception."
Sen. Patty Murray (D-WA) says ensuring that women have health care equal to men is a simple matter of fairness.
"I believe that our health care reform bill will make sure that women get access to the health care that they need, the same as men do every day," she said.
But does Congress need to be having this debate at all?
Mellman says a poll he did recently for the National Women's Law Center found that 75 percent of respondents would prefer to have an independent commission of medical professionals and citizens, rather than lawmakers, make decisions about what should or shouldn't be covered.
"They do not want politicians making health care coverage decisions. In fact, they want to keep politicians as far away from these coverage decisions as possible," he said.
Politicians, however, have a habit of not delegating decisions to others — particularly decisions regarding hot-button issues like abortion.