The polarization of American politics has characterized campaigns and elections for over a decade. 1 We have seen this in party identification, campaign messaging, voting laws, and campaign finance. Yet polarization does not explain all of what has happened over the last decade. If it did, Democrats would control all three branches of government. In public opinion polls, the number of Americans who consider themselves Democrats or Democratic leaners has exceeded those who consider themselves Republicans or Republican leaners over the last two decades. 2 The reason Republicans control the White House, and both the House and Senate going into the 2018 congressional elections, is because campaigns matter.