The midterm elections did not give Democrats a singular leader to rally behind, nor did it settle ideological divides in the party. But the results can tell us a lot about the mood among Democratic voters, and what they might be looking for in a 2020 presidential nominee. First, much hay has been made about the choice between progressives on one hand and moderates or “centrists” on the other. You could read the midterms results as vindication for the latter; outspoken progressives like Kara Eastman in Nebraska’s 2nd Congressional District and Leslie Cockburn in Virginia’s 5th Congressional District fell short,...