Updated 6:18 p.m. ET
Sources tell CBS News that Connecticut Sen. Joe Lieberman will announce Wednesday that he will not seek reelection in 2012.
Lieberman, an independent who caucuses with Democrats, is holding an event in Stamford tomorrow at 12:30 p.m. Eastern Time to announce his plans for 2012.
The controversial senator and former presidential and vice presidential candidate would face a tough campaign if he does seek a fifth term. The former Democrat, who ran successfully as an independent after losing the Democratic primary to Ned Lamont in 2006, has angered liberals with his moderate policy positions on a number of issues. They include his opposition to the "public option" in health care reform, his strong support for the Iraq and Afghanistan wars, and his support for GOP Sen. John McCain in the 2008 presidential contest.
Republicans, meanwhile, are not necessarily eager to embrace the man who joined Al Gore in the Democratic presidential ticket in 2000 and recently shepherded "Don't Ask, Don't Tell" reform through the Senate.
Former secretary of the state Susan Bysiewicz announced today that she would seek the Democratic nomination next year, and House Democrats Chris Murphy and Joe Courtney are also considering running. Former Senate candidate Linda McMahon may run for the GOP nomination. Lieberman indicated last month that if he did run again it would likely be as an independent.
An October survey by Public Policy Polling, a Democratic-leaning firm that conducts automated polls, put Lieberman's approval rating at just 31 percent. Sixty-six percent said they planned to vote to replace him, while just 24 percent said they would vote to reelect him.
Lieberman, who is 69, would be the third senator to announce in recent days that he or she will not run in 2012, joining Texas Republican and North Dakota Democratic.