Paul Waldman: Why Mark Kelly would be a trailblazing senator

While everyone is starting to think about the 2020 presidential race and consider what the Democratic candidates are proposing to do if they win, there's an unspoken presumption behind their ambitious plans, that they would actually stand some chance of passing through Congress. That will only happen, however, if Democrats control both houses.Which means that the contest for the Senate, which Republicans now control by a 53-47 margin, will be nearly as important as the presidential race.Democrat