Highly nationalized races are bad for the Senate Democrats.
To the question of just how nationalized this election is. The Democrats have to hope that the answer is, "not too nationalized." That's because in recent years, their capacity to compete in the Senate has depended on winning a set of states that lean slightly Republican relative to the nation as a whole. So if the GOP wins the Senate races in every state where they do better than they do nationwide, they will take home states including Nevada, Pennsylvania, Wisconsin, Michigan, and Arizona, all of which have Senate races up tonight.