Compromise is critical to democratic policymaking, but it can be hard to find on Capitol Hill. In this era of routine legislative gridlock, however, some lawmakers do still cross the aisle. In Dealmakers, David C. Barker, Andrew M.O. Ballard, and Christopher Jan Carman examine why they do-and why they tend to be Democrats. The answer, the authors contend, comes down to voter differences in personality and values. Specifically, they argue that empathetic traits and values drive Democrats to accept compromise, whereas competitive traits and values drive Republicans to reject it. Those differences filter up through the ballot box, the data suggest, guiding behavior in the halls of Congress. Drawing on evidence from opinion surveys, randomized experiments, Twitter/X, and legislative records, Dealmakers is the first analytical deep dive into the psychological factors that structure political dealmaking and its absence.