A quote from Majority Leader Harry Reid, D-Jellyfish:
"Joe Lieberman is a Democrat and a member of this caucus."
Hm. Last I checked, Lieberman was officially registered as an "Independent Democrat". Last I checked, he was elected not as a member of the Democratic Party but of the [Connectictut for] Lieberman Party.
UPDATE: I notice in the video that one of the Democrats standing behind Lieberman is Sen. Dick Durbin of Illinois. Funny thing: Just this summer at the Big Tent at the DNC, he couldn't name a single critical vote that Democrats had passed because of Lieberman's support. And then got nasty about it.