I can't think of an example where he pulled his schtick on a liberal.
He did have run-ins with Ted Coppel and Bernie Sanders, but otherwise all of his targets have been Republicans or conservatives, some well known, others quite obscure.
You might well wonder how it is that this Englishman actually knows anything about the little-known Republican Congressmen that he pranks or punks.
I think he's more of a snob than anything else -- anybody who didn't go to Oxbridge and anything too American are targets for him -- but that he's hired somebody who's a lot more politically motivated than he is and picks out his targets for him.