text: Lieberman is NOW an independent or an "unaffiliated" member of the senate, meaning he doesn't belong to any recognized party.  There for, in order to determine the senate majority and which party has control, he has to caucus with one side or the other, either the republicans or democrats (He really doesn't have to, but with only one other independent in the senate, HE HAS TO!) And sense he is a liberal and former democrat he will caucus with the dems.