Throwing Senator Lieberman out of the Democratic caucus would be short-sighted and irresponsible. While the majority of Democrats disagree with Senator Lieberman over foreign policy and national security, he'll nonetheless be an essential vote for domestic policy. That includes the economy, health care, vet issues, immigration and I suspect energy as well. Furthermore, it would serve no real purpose but to "set an example" that the American people may not want to see after decades of hyper-partisanship and after a promise of bipartisanship.
Senator Lieberman chairs two important committees. The GAO and the Homeland Security committees. Removing Senator Lieberman from both chairmanships would be difficult. Not only can Senator Lieberman resist, with support from centrists and Republicans and Dodd and Obama and Clinton, but he can cause a backlash for Harry Reid's leadership. People may not understand the importance of Senator Lieberman as an emissary of sorts to a limited number of Republicans. Consider the following;
While Boehner and the RNC were screaming about Rahm Emmanuel, Lindsey Graham was talking about what a fine choice Rahm Emmanuel is.
While Boehner and the RNC were criticizing Barack Obama after his victory, John McCain was pledging to work and support the President-Elect.
The Three Amigos exist. Graham/McCain/Lieberman are a trio, and will be vital if the Democrats need to enforce cloture. McCain has sent signals that he wants to return to "the old McCain." Graham has been unusually kind towards the President-Elect. It's highly unlikely that we'll have a 60 seat majority, and gaining one without Lieberman won't be possible until at least 2010. It is therefore important to keep a working relationship with those three, along with other moderates such as the two Republican ladies from Maine.
Democrats should ask Lieberman to either make a choice between his chairmanships, or they should decide for him which he can keep. Allowing Senator Lieberman to keep a single chairmanship and thereby keeping the Three Amigos close to the next GOP would be the right choice of an administration and governing party that is results-oriented. Securing votes within the Democratic Party will not be enough for a President-Obama to pass all of his plans, and is far more important than "getting even" over what was hardly a Zell Miller performance at the Republican Natinal Convention.