It turns out that Senator Joseph Lieberman is not as sure about staying the Democratic party as he may have led us to believe after a big Dem win on election night. He now says that he has not ruled out caucusing with the Republicans. If he did choose to do so, it would give the GOP a 51-49 edge over the Dems.

Lieberman is a seasoned politician, and this is clearly just politics. Joseph Lieberman is not a Republican any more than Nancy Pelosi. The only thing they shared was a view on Iraq, which caused the Democratic voters to rebel against him. Lieberman knows that now he has won his Senate seat as an Independent, he can dangle that in front of Dems whenever he's not getting his way. They don't want to give up their majority, so they'll have to make concessions to Lieberman to keep him on their side. It's a beautiful move.
Lieberman won't rule out GOP caucusing - The Boston Globe