WASHINGTON Senator Joe Lieberman, the 2000 Democratic vice presidential nominee who crossed the political aisle to back Republican John McCain in 2008 White House race, plans to announce on Wednesday that we won't seek re-election next year, a Lieberman aide said late on Tuesday.
Lieberman, 68, bolted the Democratic party to become an independent five years ago but still often sides with his old party. He plans to declare his political intentions for 2012 at a news conference in his home state of Connecticut.
"Senator Lieberman will announce tomorrow that he won't run for re-election in 2012," said the aide, who asked not to be identified by name.
Earlier on Tuesday, Democratic Senator Kent Conrad, 62, who's led efforts to get the U.S. budget under control, said on Tuesday that he will not run for a sixth term in the Senate in 2012.
"It is more important I spend my time and energy trying to solve these (budget) problems than to be distracted by a campaign for re-election," Conrad said in a statement.
Democrats now control the Senate 53-47. There are 51 Democrats and two independents -- Lieberman and Bernard Sanders of Vermont, both of whom caucus with Democrats.
Republicans are seen as having a good chance of taking the seat in conservative North Dakota, while Democrats are likely to capture Lieberman's seat in what long has been a moderate to liberal Northeastern state.
Democratic Party aides said on Tuesday that if Lieberman were to seek a fifth Senate term he would likely be defeated, having angered both Democrats and Republicans in recent years.
But the Lieberman aide said that the senator "is confident he could have won. He's had tougher fights."
The aide said that Lieberman, after more than two decades in the Senate simply "wants to open a new chapter in his life."
Lieberman has not decided what he will do next but wants to remain active in areas where he's taken the lead in the Senate in recent years, including energy and the environment, homeland security and national security, the aide said.
"The senator feels he's at a good place in his life," the aide said. "He feels very good about what he's been able to accomplish."
Lieberman has been a major figure in the Senate during his four terms. One of his latest achievements was building bipartisan support late last year to win passage of legislation backed by the White House to rescind the U.S. military's "Don't Ask, Don't Tell" policy against gays serving openly in its ranks.
Lieberman, who in 2000 was then-Democratic presidential nominee Al Gore's running mate, narrowly won a fourth Senate term in 2006 after losing the Democratic primary and becoming an independent.
In 2008, Lieberman bucked his old party and endorsed Republican presidential nominee McCain, a long-time Senate colleague and close friend, over Democrat Barack Obama.
Conrad's decision to leave the Senate at the end of his current term follows warnings he gave about the U.S. fiscal woes that led creation of a presidential commission that recommended last year spending caps and a revamped tax code.
The commission's plan could form the basis for deficit-reduction efforts in Congress as lawmakers seek to bring down shortfalls that have reached 9 percent of GDP in recent years.
As chairman of the Senate Budget Committee, Conrad will likely play a key role in the battle over federal spending during his final two years in Congress.
Conrad likely would have faced a tough re-election fight in his rural state. Fellow North Dakotan Byron Dorgan, also a Democrat, retired from the Senate last year.
In October, the non-partisan Public Policy Polling put Lieberman's statewide approval rating at 33 percent, with 54 percent of voters disapproving of him.
On Tuesday, Democrat Susan Bysiewicz, former Connecticut secretary of state, announced she would run for Lieberman's seat.
(Reporting by Andy Sullivan and Thomas Ferraro in Washington and Ros Krasny in Boston; Editing by Mark Egan and Eric Walsh)