Senator Joe Lieberman will announce tomorrow (from all reports) that he will not be seeking another term in the Senate. Democrats across the land are collectively heaving a large sigh of relief at the news. "So long, Joe," seems to be the prevailing sentiment, although if you listen closely you can hear the muttered "... don't let the door hit you on the way out," or other less-than-endearing sentiments.

Joe Lieberman's legacy will be one of a decidedly mixed nature. One might almost say "quixotic," especially in the past few years. From the heights of the Democratic Party to being little more than a pariah, Joe has charted his own course in the past decade. In 2000, Lieberman was named as Al Gore's running mate. Being a candidate for vice president launched his own presidential run four years later. But from there it was mostly downhill, in terms of how he was viewed within the party. Lieberman so annoyed his own state's Democratic voters by his staunch support of Bush's wars that he was defeated in the 2006 Democratic Senate primary, in his last bid for re-election. Joe then formed his own party and won as a third-party candidate (helped by an extremely weak Republican in the race). But even all of these were minor transgressions which could have been overlooked by Democrats. What happened next was not.

Lieberman burned his bridges with the Democratic Party in a big way in 2008, by not just endorsing and campaigning for the Republican nominee for president, but by exacerbating the situation by speaking at the Republican National Convention that year. He was even seriously spoken of as a contender for the Republican vice-presidential slot on McCain's ticket, which shows how far away he had moved at that point from the Democrats.

After Barack Obama's victory, Lieberman was excoriated for his behavior in the campaign, and most Democrats wanted to see his Democratic seniority stripped from him in the Senate as a fitting punishment (Lieberman chairs a very important committee, which he would have lost). After all, the reasoning went, if he's now an Independent, then he has no more seniority as a Democrat. Obama and Senate Majority Leader Harry Reid decided not to take this route, however, which may have been the smart move since there were rumors flying at the time that Joe was thinking of cutting all ties to the Democrats and caucusing as a Republican. If he had done so, the Democrats never would have had their brief 60-seat majority, and likely wouldn't have gotten the healthcare reform law passed.

But what did get passed was considerably weakened by Lieberman, the week before Christmas in 2009. A compromise had been reached which would have created a Medicare buy-in, which would have been welcomed by those pushing for a "public option." Lieberman himself previously had supported the concept, but for his own unfathomable reasons decided to latch onto this issue as the price of his "Yea" vote for the whole measure. It is not much of an exaggeration to say that Lieberman single-handedly killed the last, best chance for any sort of public option at all.

Thanks, Joe. Thanks a lot.

Lieberman, since then, has improved his standing among Democrats, ultimately voting for the healthcare law, and supporting the Wall Street reform law as well. His crowning achievement of last year came late, in the lame duck session of Congress, as he became the driving force behind the repeal of the "Don't Ask, Don't Tell" policy of not letting gays serve openly in the military. The last column I wrote which focused on him was titled "Thank You, Joe Lieberman," which gave him credit for this accomplishment.

At the time, some saw this as a cynical political ploy in an attempt to sway Connecticut voters to give Joe one more term in office. Looking back, it seems this was not the case. Lieberman would have had a serious uphill climb, even with the DADT repeal under his belt. Most polling in Connecticut showed that he would likely have been defeated in the primary (once again) if he had chosen to run as a Democrat -- and this time around the Republicans would not be putting up a mere token candidate, so it also would have been likely that Lieberman would have lost another third-party bid (and possibly even handed the seat to the Republicans, as a direct result).

Instead, Joe Lieberman is choosing to bow out early. Like his Nutmeg State senatorial colleague Chris Dodd, Lieberman apparently knows how to read polling results. By stepping down early, he will clear the Democratic field for a primary race to replace him. By leaving the waters thus unmuddied, whichever Democrat gains the nomination will likely have a much better chance to hang onto Lieberman's seat. So his graceful (and early) exit from the running can also be chalked up as a positive when figuring Joe's legacy.

Of course, Lieberman has two more years of voting left in the Senate before he exits. One assumes that without the pressure of facing the voters again, Lieberman will be left to vote his conscience on whatever contentious issues arise. But that's kind of the problem -- at this point, even the politics-watchers in Connecticut really have no idea what this could mean. Lieberman has been so erratic in what he supports -- flip-flopping on issues for seemingly no reason at all -- that he will still bear watching during his swansong period.

Joe Lieberman has led Democrats on such a rollercoaster ride of ups and downs over the past decade that it is impossible to predict how it will all end. But tomorrow we should at least have the answer to when it will end. We don't know now whether, in two years' time, we'll be saying it with a sarcastic sneer, or whether it will be heartfelt and well-meaning -- but we do know that in two years we'll all be saying (in one way or another):

"So long, Joe."

-- Chris Weigant

Follow Chris on Twitter: @ChrisWeigant