The problem is that Joe’s vote will actually become more important the more that Democratic majorities expand. More precisely, the closer that the Dems get to the magic number (60), the more vital Joe becomes. Ironically enough, I think Lieberman is more important in a 59-41 Senate than in a 53-47 one.
I understand the sentiment and the logic behind this rationalization but I think Publius is over-thinking this. From a purely objective mathematical standpoint Joe Lieberman is less important to Democrats if we have 57 or 58 seats than he is now. That's just cold hard mathematical reality.
Publius' argument gets, I think, a little lost in the weeds. There's a very simple, clear reason why Lieberman should get the boot - he chairs a very important committee (Homeland Security and Governmental Affairs) and has not conducted any oversight of the Bush administrations war conduct whatsoever.
He's been very, very bad at his job and he should be removed for that reason alone. There's no reason for a party with a significant majority to be held hostage by a guy who's not interested in doing his job.