Senator Lieberman says he is going to run as an independent, having lost the Democratic Party nomination in Connecticut.
I don't know much about how party discipline works in the US, but in the UK running against an official party candidate would lead to automatic expulsion from the party.
As far as I know, Senator Lieberman is currently the ranking Democrat on the Senate Homeland Security committee, and he sits on the Armed Services, Small Business, and Environment Committees. According to the BBC:
Meanwhile Senate Democratic leader Harry Reid of Nevada and Sen Chuck Schumer of New York – the chairman of the party's Senate campaign committee – have pledged their full support for Mr Lamont.
I wonder if Senator Reid's support for Mr Lamont includes removing Senator Lieberman from his committee posts?