In your typical midterm election with an unpopular Democratic president, you’d expect Republicans to be flying high. But the evidence is mounting that the national political environment right now actually leans toward Democrats. On Tuesday, Democrat Pat Ryan defeated Republican Marc Molinaro in a special election for New York’s swingy 19th Congressional District by 2 percentage points, 51 percent to 49 percent.1 At the same time, Republican Joe Sempolinski defeated Democrat Max Della Pia by a closer-than-expected margin of 7 points in the special election for New York’s solid-red 23rd District. On their own, these elections could be dismissed as...