Republicans try to placate the Left in the Senate by picking “conservative” justices that can pass muster as not being TOO conservative. Liberal presidents on the other hand pick the most liberal justices they can find because they know the Republican Senators like Dick Lugar will do the advice and consent thing and then vote for anybody the president chooses whether they agree with the nominees views.
So indirectly they are co-conspirators - a faction in this corrupt "Two-Party Cartel".