Presidential elections are arguably the most consequential recurring political event in the United States. Understanding the factors that determine their outcomes, therefore, is of substantial importance. One proposed factor pertains to candidates’ incumbency status, yet its nature is complex and difficult to study with observational data. In particular, the individual-level mechanisms underlying incumbency effects remain surprisingly unclear. This Letter proposes many citizens generally believe that, ceteris paribus, presidents should be afforded two terms. Existence of such a norm implies that incumbency status possesses an inherent effect, operating independent of other mechanisms stemming from incumbency. A large, pre-registered survey experiment is employed to isolate incumbency status, finding evidence for a one-term advantage and clarifying the nature of the two-term disadvantage. The study thus uncovers a micro-foundational mechanism underlying incumbent-party performance in presidential elections. Finally, analyses of panel data explore which voters may be systematically inclined to vote based upon incumbency status.