A VANITY EXERCISE?…. A week ago, when Sen. Joe Lieberman (I-Conn.) announced that he intended to join a Republican filibuster of health care reform, Senate Democrats and the White House were oddly serene. Just a day after Senate Majority Leader Harry Reid (D-Nev.) unveiled the reform bill, Lieberman was already threatening to derail the entire effort — and party leaders more or less shrugged.

That afternoon, reporters asked Reid about the likelihood of a Lieberman betrayal. “Joe Lieberman is the least of Harry Reid’s problems,” he replied.

Does Reid know something about Lieberman the rest of us don’t? Actually, he might.

Sen. Joe Lieberman has reached a private understanding with Majority Leader Harry Reid that he will not block a final vote on healthcare reform, according to two sources briefed on the matter.

The unpredictable Democrat-turned-Independent last week publicly stated he would join Republicans in filibustering the Democratic legislation after Reid (D-Nev.) announced he had included a government-run health insurance plan in the bill.

But sources said Reid’s staff is telling liberal interest groups that Lieberman (Conn.) has assured Reid he will vote with Democrats in the necessary procedural vote to end debate, perhaps with intentions to change the bill.

“At the end of the day Sen. Lieberman will vote to cut off debate,” said Richard Kirsch, national campaign manager of Healthcare for America Now. “He’ll do what he has to do. He’s making a lot of noise.”

I can only hope this confidence is not misplaced. A whole lot is riding on an expectation that Joe Lieberman will not choose betrayal over progress.

Of course, if the scuttlebutt is right, and when push comes to shove, Democrats can count on Lieberman at least voting for cloture, what’s the point of the Connecticut senator’s bluster? A few things may be motivating him. For one thing, Lieberman sees an opportunity to drag the reform bill to the right, so he’s taking advantage of it. For another, he’s picking up bargaining chips he can use now and in the future.

But perhaps most important is the fact that Joe Lieberman enjoys vanity exercises. By threatening to kill health care reform, Lieberman gets attention. He feels important. His phone keeps ringing. People want to know how to make him happy. He gets to go on television a lot. As Lieberman declared late last week, “I feel relevant.”

Lieberman is, in other words, November’s Olympia Snowe.

For the record, I’m not at all convinced that Lieberman is going through the motions and will do the right thing in the end. Indeed, it’s an odd defense — “Don’t worry,” we’re told, “Lieberman is totally insincere.”

But if Lieberman is saying one thing in front of the cameras, and something else to Reid behind the scenes, then there’s reason for at least some optimism about how this will play out.

Update: A Senate leadership aide told me this morning that Reid does “not yet have an understanding” with Lieberman. What’s more, Lieberman’s spokesperson told National Review that the reports are “absolutely not true.”

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

Steve Benen

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.