Greg Sargent gets it in his "memo" to the Times:

[I]t's really, really critical that the paper be more skeptical when reproducing the storyline that Lieberman may leave the Democratic Party, and hence, that he alone holds the fate of the Dems in his hands. Mr. Taubman and Ms. Abramson, this is exactly the story Lieberman wants you to tell. But the truth is this: Lieberman is virtually certain not to switch. The Senate map for 2008 looks like tough sledding for the GOP, so if Lieberman switched parties, he'd be at grave risk of relegating himself to the minority for years to come. And as you've probably noticed by now, the last thing Lieberman wants is to be considered irrelevant. Every time he hints that he might switch, he's doing it to get attention -- nothing more, nothing less. Why would you allow yourselves to be played for suckers in this manner for two days in a row now?