Lieberman won his fourth term in 2006 as an independent.
Lieberman almost won the vice presidency on the Democratic ticket in 2000 and he had an unsuccessful presidential bid in 2004.
Sen. Joe Lieberman confirms 2012 retirement
STAMFORD, Conn. Democratic officials had said on Tuesday that Lieberman was planning to retire. The 68-year-old senator will not be seeking re-election to a fifth term, according to a statement by his office.
