FULL NELSON…. Just a week ago, Sen. Ben Nelson of Nebraska, the chamber’s most conservative Democrat, said he would likely join a Republican effort to kill health care reform unless the bill featured the Stupak amendment language. Late yesterday, the Senate rejected Nelson’s push anyway — 45 senators voted to add the measure to the bill, 15 short of what was necessary.

So, where does that leave us? Nelson did not, in the wake of his amendment’s defeat, announce that he would join the GOP filibuster. Instead, the Nebraskan said the vote “makes it harder to be supportive” of the bill. Asked if he now opposes the legislation, Nelson said, “Not at this point in time.”

Roll Call reports that some Democrats on the Hill believe that Nelson’s support is slipping away, and suspect he may side with Republicans to deny health care reform an up-or-down vote.

In their quest to secure a filibuster-proof 60 votes for the overhaul, Democrats said Nelson’s support was appearing unattainable — with or without the inclusion of his abortion provisions — given the myriad objections he has to other parts of the bill, including the creation of a public insurance option.

“The concern about Sen. Nelson is that he’s gotten himself pretty far out on a couple of limbs,” said one senior Senate Democratic aide. […]

Democrats privately said they do not think Nelson will end up voting for the health care overhaul, and the likelihood of losing both Nelson’s and Lieberman’s votes is very real.

“I think we lose one of the two of them for sure,” said the senior Senate Democratic aide. “If I’m reading it right, we lose Nelson for sure, and there’s a greater than 50 percent chance we lose Lieberman, too.”

Now, the Roll Call piece was, I believe, written before the new compromise on the public option was reached, which may change the larger dynamic. Indeed, for both Nelson and Lieberman, the top demand was the defeat of the public option. The measure has clearly been changed dramatically.

Let’s not forget that just a few weeks ago, Nelson said he doesn’t like the existing restrictions on abortion funding, but added, “If there’s no public option, perhaps some of the [abortion] problem goes away.” Since he’s signaled at least some support for the compromise, perhaps last night’s deal will keep him in the fold. Or, perhaps not. We’ll see.

Obviously, arithmetic being what it is, losing either Nelson or Lieberman makes Maine’s Olympia Snowe and Susan Collins that much more important. Indeed, because the Senate no longer operates on majority-rule, losing Nelson and Lieberman would make the only two Republican moderates entirely necessary to prevent the death of the bill.

Our ideas can save democracy... But we need your help! Donate Now!

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.