Sen. Ben Nelson (D-Neb.) insisted this week that while he still supports the Democratic health care reform effort, his vote is far from a sure thing.

Nelson was the critical 60th vote for the Senate overhaul late last year, and he has been taking a beating ever since. In addition to supporting the $871 billion measure itself, Nelson has come under fire for securing two key provisions — one that stiffened access to abortion and another that required the federal government cover Nebraska’s portion of a Medicaid expansion.

Still, Nelson isn’t making apologies. He reiterated Wednesday that Senate Majority Leader Harry Reid’s (D-Nev.) 60-vote coalition would shatter if a public insurance option — favored by most House Democrats, including Speaker Nancy Pelosi (Calif.) — makes the merged package. And he said his vote hinges equally on the abortion language.

“Those were the deal-makers and the deal-breakers,— Nelson said in a telephone interview from his home in Omaha. “I’ve been very clear to the White House and to leadership.—

Nelson won’t say how he’ll vote when the House and Senate merge their two competing versions. Likewise, he won’t say whether he is going to insist that all 50 states get the same Medicaid deal he got, nor will he say whether he would accept a national insurance exchange as a part of the reconciled bill being negotiated by House and Senate Democratic leaders and the White House.

As part of his deal with Senate leaders, Nelson secured a $100 million provision to cover Nebraska’s cost of a proposed Medicaid expansion. The provision has been coined the “Cornhusker Kickback,— and several Democratic Members have demanded it be stripped from the final House-Senate package.

Sen. Blanche Lincoln (D-Ark.), also on the defense at home for supporting health care reform, recently accused Nelson of “horse trading— and said there’s no place for special deals in major policy overhauls. And Tuesday evening, some Democratic Congressmen lashed out at Nelson, blaming him and other moderate Senate Democrats for poisoning the cross-chamber health care negotiations.

“The Senate is just a pain in the ass to everybody in the world as far as I can tell. I’m so angry that I just wish from now on that we’d just find out what it is that [Sen. Joe] Lieberman [ID-Conn.] and Nelson will let us have,— one senior House Democrat said.

Nelson, a former governor with a long history of opposing unfunded federal mandates, now claims that “there is a lot of misunderstanding— surrounding the Nebraska Medicaid provision, including what his intent was when he proposed it and how it ended up in the Senate bill. Nelson said he intended for the provision to act as a placeholder to ensure that all states would ultimately get the same Medicaid coverage in the final bill.

Nelson said “the leadership put it in,— but that he doesn’t know who in particular, and said he asked for less than $100 million for his state. Nelson said he has been in contact with Reid and Obama since the Senate bill passed on Christmas Eve and has been assured that all states will be treated equitably in the final package. Reid’s office declined to comment on the matter.

“It had nothing to do with my vote,— Nelson insisted Wednesday, emphasizing that his goals were strengthening the abortion restrictions in the bill and killing the public insurance option.

Nelson, however, wouldn’t say what lines he would draw going forward. He refused to comment on whether he would support the bill if the Medicaid provision were axed, nor would he comment on how he would respond if Democratic leaders didn’t extend it across the board, a move that would add nearly $30 billion to the measure’s price tag.

“That’s not being discussed, so I’m not going to answer,— Nelson said.

Meanwhile, Nelson appeared to dismiss the idea of creating a national insurance exchange under which Americans could purchase coverage. The proposal is being floated as a potential compromise between the House and Senate bills. The Senate measure calls for state exchanges, while the House legislation includes a nationwide public option.

A centrist Democrat from a reliably conservative state, Nelson typically finds himself at the center of negotiations involving politically charged legislation. But in his eight years in the Senate, he has managed to prevent his vote from being perceived as the determining factor to a bill’s success — until now.

Late last month, with hours to go before Reid planned to file a series of three cloture motions to clear the health care legislation, Nelson was the lone Democratic holdout. But on Dec. 18, after days of marathon negotiations with party leaders on an abortion language compromise, he jumped aboard.

Nelson acknowledged that the 11th-hour deal-making is responsible for his political headache, and he said it probably happened “because I took such a strong stance on abortion — maybe the strongest.—

“I didn’t seek it. I didn’t set out to be the 60th vote,— Nelson said.

Rep. Bart Stupak (D-Mich.), who opposes abortion rights and inserted similar abortion language into the House health care bill, has since declared Nelson’s compromise unacceptable.

David Di Martino, Nelson’s former deputy chief of staff, said his one-time boss ended up in the spotlight because Republicans were committed to opposing health care reform. All 40 GOP Senators opposed the bill through three cloture votes and on final passage.

Di Martino said Nelson has usually worked with Republicans on bipartisan alternatives to controversial proposals, ranging from tax-cut legislation and judicial nominations to last year’s $787 billion economic stimulus package. This time, Nelson had no willing GOP partners.

“In this case, he was working with Republicans in good faith, but they dug in,— argued Di Martino, who now runs a downtown consulting firm. “He was trying to find a way to make this bipartisan. That didn’t happen, and he was left standing alone.—

Nelson appears to have maintained his usual calm even as he comes under fire. But he is not dismissing the potential political perils of his health care vote.

Since returning home for the holidays, Nelson has run television ads explaining his vote and has sought out newspaper, radio and television interviews in every corner of the state. Republicans contend Nelson is in considerable trouble, although they concede he could be fine by 2012, when he is next up for re-election.

Nelson said he has survived controversy before and expects to be just fine once all of the facts of the health care bill are understood. “There’s a lot of misunderstanding,— he said. “With all of these opinions floating around … it’s obvious people are confused.—

“These things come and they go,— Nelson said.

For all of the criticism he’s received, Nelson said many of his constituents have thanked him for his vote and urged him not to back down.

And although Nelson has speculated publicly that the country might have been better off had Congress simply focused on jobs and the economy rather than health care, he decided he couldn’t vote “no— on the legislation in light of the hundreds of thousands of uninsured Nebraskans.

Republicans “have taken the approach of no to everything,— Nelson said. “They’re staking their future— on this strategy.

Jennifer Bendery contributed to this report.