What we know for sure is that Joe Lieberman will announce his intentions on 2012 and re-election at an event in Connecticut tomorrow. What we don’t know for sure is what he’ll say, but insiders in Connecticut from both parties think he’ll retire. Republican operative Kevin Rennie:

United States Senator Joseph Lieberman (I-CT) is expected to announce Wednesday that he will not seek a 5th term in 2012, Daily Ructions has learned. Lieberman has invited supporters to an event at the Marriott hotel in Stamford Wednesday afternoon for his announcement.

Democratic operative Patrick Scully:

US Sen, Joseph Lieberman will announce tomorrow that he is not seeking reelection sources close to the four-term senator have told The Hanging Shad. Lieberman plans to make clear that he is not seeking another term at a formal announcement tomorrow at 12:30 pm at the Stamford Marriot.

…sources close to Lieberman tell The Hanging Shad it’s apparent to the senator that he doesn’t have the base to run. His approval rating in the last Quinnipiac poll was 40%. He angered many in the Democratic establishment by speaking at the 2008 Republican National Convention and by campaigning for Republican nominee John McCain. And with 2010 US Senate Republican nominee Linda McMahon waiting in the wings for another try, Lieberman would not be able to put together the coalition of Democrats, Republicans and Independents with which he won in 2006 after losing the Democratic primary to Ned Lamont.

This comes a day after former Connecticut Secretary of State Susan Bysiewicz announced that she would run for the seat. Other Connecticut Democrats have mulled over a run, including Reps. Chris Murphy and Joe Courtney. On the Republican side, Linda McMahon could give it another shot, along with former Rep. Rob Simmons, who dropped out of a Senate bid when McMahon won the state party endorsement last year, and then tried an ill-fated last-minute return to the race.

Coming on the heels of Kent Conrad’s retirement today, I imagine this will lead to more speculation about “Democrats in disarray.” But this announcement by Lieberman, if it goes as expected, would be a win not just for the mainstream Democratic Party, but the progressive wing of that party. Republicans couldn’t win statewide in Connecticut even in the very favorable election of 2010, and with Obama on the ballot, Democrats would begin very likely to hold the seat. And getting Lieberman out of the picture is a victory for virtually everyone. There’s been a 6-year delay, but ultimately this is the final result of the 2006 primary won by Ned Lamont. Lieberman had no base of support in the Democratic Party ever since winning the general election in 2006, and his fluke coalition couldn’t hold no matter what he tried.

The only bad part of this expected announcement is that Joe Lieberman won’t just walk out tomorrow and not further darken the doors of the US Senate. Connecticut can do much better.

UPDATE: More from Ryan Grim.

UPDATE: Looking more and more like Lieberman will call it quits.