Im glad both you and Lorax are showing a teenie weenie bit of tolerance towards Joe ... who is a Lefty Democrat on just about every issue except the War.
Lieberman's basic ideology is in line w/ the Dems, save the rather huge exception of the war. It has never made sense that he would join the GOP, because his domestic views are so completely off-kilter w/ their platform. He would continue to vote with the Dems over 90% of the time, unless he completely sold out his principles.
It's the way he conducted himself in the campaign that nags at most Dems. It's one thing to endorse a candidate of the opposing party; it's quite another to actively campaign for that candidate, and also to speak at the RNC. All of that could still be forgiven, imo, if he didn't ALSO jump on the bandwagon of questioning Obama's character and tearing into the idea of Obama as a potential President. He definitely crossed a line, and if he dodges this bullet by virtue of the good will of Obama, he should devote the rest of his Senate career to serving the admin in the best way he can.