Incumbents significantly outperform challengers in American elections, but the implications of this phenomenon are ambiguous. Do otherwise unpopular incumbents exploit the political system to stay in power, or do open elections effectively select good candidates who will naturally win reelection? To address this question, I estimate the extent of incumbent success that can be attributed three factors — party match, characteristic selection, and officeholder benefit. Across numerous settings in the U.S., a significant portion of incumbent success can be attributed to the tendency of previous elections to select popular candidates that match the partisan preferences of voters. On average, party match explains about five-eighths of incumbent success and characteristic selection explains one-eighth, leaving only one quarter to be explained by the effects of holding office. These results also vary in meaningful ways across time periods, settings, and electoral institutions.