US senator Joe Lieberman of Connecticut, the Democratic vice-presidential nominee in 2000 who became an independent to survive a bruising 2006 Senate re- election, said he won't seek another term.
"I have decided that it's time to turn the page to a new chapter," Mr Lieberman said at a news conference in Stamford, Connecticut. He said he will serve the final two years of his fourth term before retiring.
Acknowledging he would have faced another tough campaign, Mr Lieberman insisted he isn't running from a fight and instead is seeking "another season and another purpose" after 24 years in the Senate.
His decision not to run in 2012 will mark an end to a political career in which he was a leader of Democratic centrists in the Senate before Connecticut Democrats turned against him over his support for the Iraq war.
After losing the party's Senate primary in 2006, he became an independent and won the general election. He remains a swing vote in the Senate who caucuses with Democrats.
Mr Lieberman ran as the Democratic vice-presidential nominee on the ticket headed by Al Gore in 2000. He was the first Jewish candidate on a major national political party's presidential ticket.
In 2006, he was in effect forced out of the party over his support for the Iraq war when Ned Lamont, an anti-war Democrat, beat him in the Democratic Senate primary. He pivoted and ran as an independent, defeating Mr Lamont by 10 percentage points as he won re-election with 49.7 percent of the overall vote.
Bloomberg