Joe Lieberman is the former Democratic Senator from
Tel Aviv Aetna Connecticut. He's both a former Senator and a former Democrat. He was for a long time George W. Bush's go-to guy for a Democrat who would support him on the war; when this cost him the Democratic nomination in 2006, he ran as an independent and won anyway.
The funny thing is that it was his willingness to run as an independent that cost him the nomination. With the support of Connecticut's Republicans, he barely won re-election to his seat, (by barely we mean by under 10 points).
Earlier in his career, he was well known as Al Gore's running mate in 2000 (although the "blame Nader" crowd would prefer you not mention this inconvenient truth), and for being a righteous tightass. He was the only Democrat in the Senate, except for Robert Byrd, to publicly rebuke Bill Clinton, and he privately led a crusade to get professional wrestling off of TV. His most frequently used phrase during 2000 debates with Dick Cheney was "I agree with my opponent on that." In 1988 he first won his seat running against liberal Republican Lowell Weicker by running to the right and seeking and getting the endorsement of, among others, the Moral Majority.
He was very supportive of George W. Bush and his Iraq war. He was also very supportive of John McCain, and followed him around like a puppy everywhere he went in hopes that he might become vice-president. Didn't happen.
Following his McCain endorsement, Harry Reid planned to punish Lieberman by stripping him of his seniority within the Democratic caucus and his committee assignments (including his chairmanship of the Senate Homeland Security Committee) , but Barack Obama (the man he campaigned against, mind you), talked Reid out of it, as he was apparently more interested in getting Joe to vote with the Democratic Party than in punishing him. It worked for a little bit, he was a reliable Democratic vote except on the Democrats' major issue, health care reform with a public option. On that issue he threatened a filibuster, and thus was single-handily responsible for the Public Option being removed from the final healthcare reform bill. The fact that Connecticut contains the headquarters of most of the insurance industry could possibly be mere coincidence.
Lieberman announced that he would not seek re-election and retired from the Senate, effective 2013. He was replaced by Democrat Chris Murphy.