Sen. Joe Lieberman (I-Conn.) on Wednesday afternoon formally confirmed what most of the political world already knew — that he will not seek a fifth term in 2012, ending a storied Capitol Hill career marked by a fierce independence that often put him at odds with the Democratic Party.
 
“This was not an easy decision for me to make because I have loved serving in the Senate and I feel good about what I have accomplished,” he said in prepared remarks delivered inside the Marriott in Stamford, Conn., roughly in the same area where he lived with his family in a cold-water flat as a young boy. “But I know it is the right decision and, I must say, I am excited about beginning a new chapter of life with new opportunities.”

The 68-year-old Senator largely brushed aside the looming political challenges that would have complicated any re-election effort.
 
“I know that some people have said that if I ran for re-election, it would be a difficult campaign for me. But what else is new? It probably would be,” Lieberman said.
 
“I have run many difficult campaigns before — from my first one in 1970 against the incumbent Democratic state Senate Majority Leader, to my 1988 campaign against the incumbent Republican U.S. Senator, to my campaign for re-election to the Senate in 2006 at the height of the controversy over the Iraq War. In all three of those elections, most observers and pollsters thought I would not win. But with a lot of help from independents, Democrats and Republicans — including many of you here today — in each case I did win. I’ve never shied from a good fight and I never will.”

It was widely believed that Lieberman had done irreparable damage to his one-time loyal Democratic base in recent years — most notably by leaving the party in favor of a successful Independent run after losing the 2006 Democratic primary.
 
News of his impending retirement announcement broke Tuesday night, the same day that Democratic candidates started lining up to challenge Lieberman. Longtime Secretary of State Susan Bysiewicz (D) announced her candidacy Tuesday, and Rep. Christopher Murphy (D) is likely not far behind.
 
Indeed, it was often a love-hate relationship for the left and Connecticut’s senior Senator, whose subsequent decision to caucus with Democrats allowed them to hold both a simple Senate majority and briefly a filibuster-proof majority. His position helped Lieberman secure and hold the gavel of the Homeland Security and Governmental Affairs Committee, even after he endorsed GOP presidential hopeful Sen. John McCain (Ariz.) in 2008 and was among the featured speakers at that year’s Republican National Convention. He also helped former Alaska Gov. Sarah Palin prepare for the vice presidential debate.

“Lieberman’s poll numbers were disastrous in Connecticut. His decision to quit in the face of assured defeat is a huge victory for the progressive movement and all Americans who want Democrats to put regular families ahead of corporate interests,” said Keauna Gregory, senior field organizer with the Progressive Change Campaign Committee. Gregory was already on the ground in Connecticut “ready to pounce” on Lieberman should he run, the liberal group said.

White it alienated the left, Lieberman’s independence also allowed him to wield tremendous power at times. Aside from the committee chairmanship, he served as Al Gore’s running mate in the 2000 presidential contest and was on a short list to do the same for the McCain’s Republican ticket eight years later.
 
“Along the way, I have not always fit comfortably into conventional political boxes — Democrat or Republican, liberal or conservative,” Lieberman said Wednesday. “I have always thought that my first responsibility is not to serve a political party but to serve my constituents, my state and my country, and then to work across party lines to make sure good things get done for them.”

It’s unclear how the looming retirement will affect Lieberman’s allegiances on Capitol Hill in the coming two years. His 22-year career has already been marked by high-profile breaks with Democratic leaders. He has sided with Republicans on national security issues and invited the 2006 primary challenge by backing the Iraq War. But Lieberman supported President Barack Obama’s health care overhaul and is generally a staunch liberal on social issues, such as the repeal of “don’t ask, don’t tell,” which he helped champion during the recent lame-duck session.
 
Such votes alienated Connecticut Republicans, who were a key to his success in the 2006 race that featured a GOP candidate who was little more than a placeholder.
 
State GOP chairman Chris Healy told Roll call on Tuesday that Lieberman would have had difficulty winning Republican support going forward. He noted that both independently wealthy wrestling executive Linda McMahon and the narrowly defeated gubernatorial candidate Tom Foley would have far greater appeal than Lieberman among Connecticut’s relatively small bloc of Republican voters.

Both Republicans have left open the possibility of running for Lieberman’s seat, although neither has yet to commit.
 
In some ways, Lieberman’s retirement would improve Democrats’ chances of holding the seat. Three-way races are notoriously difficult to gauge.
 
In a two-way race, however, Democrats hold a significant registration advantage, Obama carried the state by more than 20 points in 2008, and McMahon failed to win a 2010 Senate race, despite favorable conditions and having spent more than $50 million from her own pocket.

Given Lieberman’s retirement, Roll Call Politics changed Connecticut’s Senate race rating to Leans Democratic from the more competitive Tossup category.

In the end, however, Lieberman said his decision had little to do with politics.

“The reason I have decided not to run for re-election in 2012 is best expressed in the wise words from Ecclesiastes: ‘To everything there is a season, and a time to every purpose under Heaven.’ At the end of this term, I will have served 24 years in the U.S. Senate and 40 years in elective office. By my count, I have run at least 15 full-fledged political campaigns in Connecticut,” he said.
 
“For me, it is time for another season and another purpose under Heaven.”