Twice now, abortion was almost a dealbreaker. This time, it was a dealmaker. But of hundreds of deals cut so health care legislation can stay alive, the hardest to keep may be the Senate's abortion compromise _ achieved after 13 hours of negotiation. The volatile issue remains the biggest threat to getting a history-making bill to President Barack Obama.

Deals are the lifeblood of legislation. Mary Landrieu of Louisiana got $100 million more for her state, Connecticut's Joe Lieberman stripped the bill of a government insurance plan and Ben Nelson won a slew of favors for Nebraska _ all in exchange for their votes.

Nelson was also pivotal in the abortion compromise. The abortion-rights foe cast the 60th vote Monday to prevent Republicans from burying the bill.

Abortion is an issue that doesn't usually lead to common ground, since interested groups have radically opposed views. That makes the Senate compromise _ which seeks to prohibit the use of tax dollars for abortions _ rare, even surprising. It's also why, as Senate Democrats move to negotiations with the House, other deals in their bill may stick more easily.

House liberals are starting to accept that they probably won't get a government insurance plan. But abortion opponents in the House nearly stopped health care once before, and they are poised to try again to preserve their more restrictive approach. It could be a dealbreaker.

Sen. Barbara Boxer, D-Calif., represented abortion rights supporters in the negotiations only to face criticism from women's rights groups, not just abortion opponents. Now, Boxer is urging lawmakers to take a second look. "You have both sides criticizing it, which means that we did what we had to do, we compromised in a fair way," Boxer said.

Hours before the Senate's abortion compromise came together last Friday, it looked like things would fall apart. Three Democratic officials familiar with the talks detailed how events unfolded. They spoke on condition of anonymity, because the talks were private.

Obama's health care remake extends coverage to 94 percent of Americans, not including illegal immigrants, and tries to slow increases in medical costs. But in the Senate, Nebraska's Nelson stood in the way. Among his chief objections was his belief that the Senate's restrictions on government funding for abortion were too lax.

The negotiations began at 9:30 a.m. Friday in a suite of offices in the Capitol occupied by Majority Leader Harry Reid, D-Nev. Steps from the Senate floor, Reid's spacious lair is shielded from inquisitive media. There would be suspense, shuttle diplomacy, hugs, and a call from Obama aboard Air Force One before the day was done.