Democratic officials, who requested anonymity because they were not authorized to speak publicly, said Tuesday that the independent from Connecticut would not seek a fifth term in 2012.
The 68-year-old Lieberman won his fourth term in 2006 as an independent after losing the Democratic primary to businessman Ned Lamont, but he continues to side mostly with Senate Democrats.
Connecticut Democrats have been upset with Lieberman since his appearance at the Republican National Convention in 2008 and his endorsement of GOP presidential candidate Sen. John McCain.
They've also criticized his strong support of the Iraq war, although they were pleased when he led the fight to repeal the ban on gays serving openly in the military.
