The impeachment trial of President Donald J. Trump begins in earnest, and the all-important Iowa caucuses are less than two weeks away. With three of the top five presidential candidates locked in the Senate chamber hearing testimony, the Iowa race is too close to predict. Biden and Buttigieg have the state to themselves—and they're taking advantage of it—while Senators Sanders, Warren and Klobuchar must rely on surrogates at campaign events and off-hour interviews from DC.