This quote pretty much says it all:
Since his election as an independent in 2006, Lieberman has successfully reinvented himself as every Republican's favorite Democrat, always available to endorse a Republican candidate, or support the Republican position on a piece of legislation, but somehow still managing to generate more media attention because he is nominally a Democrat. Lieberman, for example, repaid that senator from Illinois for his 2006 primary endorsement by endorsing his Republican opponent in the 2008 presidential election.
It is astounding that as late as 2009, some still considered Lieberman a Democrat and believed that by offering him good committee assignments, Lieberman could be convinced to work with the Democrats on needed legislation. Lieberman's latest pronouncement makes it clear beyond a shadow of a doubt, what was clear to many a few years ago. There is no sense pursuing Lieberman's support or offering him any incentives because when he is needed most by the Democratic Party he can only be depended to abandon the party, its goals and its leaders.
More:
http://www.huffingtonpost.com/lincoln-mitchell/is-anybody-still-surprise_b_336685.html