FULL NELSON…. Expressing some optimism about the prospects of health care reform, Jon Chait said yesterday he has hard time envisioning a member of the Senate Democratic caucus casting a “vote to filibuster health care reform to death.” It’s just hard to imagine, he said, a Dem taking “the active step of killing what has been the centerpiece of the Democratic agenda for sixty years.”

Alas, it’s not that hard to imagine.

Sen. Ben Nelson (D-Neb.) says that Democratic leaders should not count on him to be the 60th vote for passing healthcare reform this year.

Nelson, who has bucked his party more than any Senate Democrat on procedural votes in 2009, is a pivotal figure on healthcare. With 59 Democrats in the upper chamber and centrist Sen. Olympia Snowe (R-Maine) in negotiations with Democratic leaders, the prospect of compiling 60 votes to overcome procedural obstacles appears within reach.

But Nelson isn’t promising anything. He told The Hill, “I’m not going to commit anything at this point in time on procedural votes, neither pro nor con, because it will depend on the circumstances. I can’t make those decisions in advance because it depends on what the bill is and what the circumstances are at the time.”

Now, this wasn’t an explicit threat. Nelson didn’t come right out and say, “I’ll vote with the GOP to filibuster a bill with a public option.” It’s more of a generic threat — Nelson might vote with the GOP to filibuster reform.

Sen. Evan Bayh (D-Ind.) signaled a similar approach. In fact, in some ways, he’s worse — The Hill reported that Bayh initially said “he considers procedural votes no different from final votes on legislation,” though he later walked that back a little.

It gets back to a point we discussed over the weekend. Ed Kilgore argued, “That Democrats could be against health reform is disappointing. That they’d deny a vote on it is unacceptable…. [T]he time has come — and in fact, it is long overdue — for them to begin forcefully making the case that being a member in good standing of the party’s Senate caucus means supporting cloture motions on key legislation even if a given senator intends to vote against it.”

This shouldn’t even be controversial — to be a member of the caucus means letting the Senate vote on Democratic bills. It doesn’t mean every Dem has to vote for every Democratic idea; it means they at least have to let the vote happen.

Nelson and Bayh don’t see it that way.

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.