Over the years we've witnessed numerous bipartisan "gangs" and every single time the Republicans steal the lunch money from the Democrats. Sometimes this is probably just a show, the Dems involved are happy to give the Republicans what they want. But quite often I think these are seemingly lonely (mostly) guys who relish the opportunity to have a few extra lunches and meetings with their pals and an opportunity to feel special for a few weeks.
You don't have to be a bit nuts to be a House or Senate member (you do have to be nuts to want to be president), but the jobs do attract some nutters. A certain kind of social weirdo who crave a bizarre kind of attention. Think Lindsey Graham. Not saying the Dems I am thinking of are like him in all ways, but in some.