The incumbent is the current holder of a political office. This term is usually used in reference to elections, in which races can often be defined as being between an incumbent and non-incumbent(s). For example, in the 2012 United States presidential election, Barack Obama was the incumbent, because he had been the president in the previous term while the election sought to determine the president for the current term. A race without an incumbent is referred to as an open seat.
The word "incumbent" is derived from the Latin verb incumbere, literally meaning "to lean or lay upon" with the present participle stem incumbent-, "leaning a variant of encumber, while encumber is derived from the root cumber, most appropriately defined: "To occupy obstructively or inconveniently; to block fill up with what hinders freedom of motion or action; to burden, load."
In general, incumbents have structural advantages over challengers during elections. The timing of elections may be determined by the incumbent instead of a set schedule. For most political offices, the incumbent often has more name recognition due to their previous work in the office. Incumbents also have easier access to campaign finance, as well as government resources (such as the franking privilege) that can be indirectly used to boost a campaign. An election (especially for a legislature) in which no incumbent is running is often called an open seat; because of the lack of incumbency advantage, these are often amongst the most hotly contested races in any election.
In the United States, incumbents traditionally win their party's nomination to run for office. Unseating an incumbent president, governor, senator or other figure during a primary election is very difficult, and even in the general election, incumbents have a very strong record. For instance, the percentage of incumbents who win reelection after seeking it in the U.S. House of Representatives has been over 80% for over 50 years, and is often over 90%. However, this rate may be artificially inflated, as incumbents that feel unlikely to win may decline to run for reelection. Additionally, shifts in congressional districts due to reapportionment or other longer-term factors may make it more or less likely for an incumbent to win re-election over time. For example, a Democratic incumbent in historically conservative rural Texas would have less chance of winning than a Democratic incumbent in historically liberal New York City, because Texas has shifted away from the Democratic Party in terms of voting while New York City has shifted toward the same party (see also Congressional stagnation in the United States).
When newcomers look to fill an open office, voters tend to compare and contrast the candidates' qualifications, issues positions and personal characteristics in a relatively straightforward way. Elections featuring an incumbent, on the other hand, are as Guy Molyneux puts it, "fundamentally a referendum on the incumbent." Voters will first grapple with the record of the incumbent. Only if they decide to "fire" the incumbent do they begin to evaluate whether the challenger is an acceptable alternative.
A 2017 study argues that the incumbency advantage stems from the fact that voters evaluate the incumbent's ideology individually whereas they assume that the challenger shares the party's ideology. This explains why higher-profile Senate races have less incumbency advantage than low-profile races in the Senate and the House of Representatives. This also means that the incumbency advantage gets more significant as political polarization increases.
Political analysts in the United States and United Kingdom have noted the existence of a sophomore surge in which first term representatives see an increase in votes in their first election. This phenomenon is said to bring an advantage of up to 10% for first term representatives, which increases the incumbency advantage.
However, there exist scenarios in which the incumbency factor itself leads to the downfall of the incumbent. Popularly known as the anti-incumbency factor, situations of this kind occur when the incumbent has proven himself not worthy of office during his tenure and the challenger demonstrates this to the voters. An anti-incumbency factor can also be responsible for bringing down incumbents who have been in office for many successive terms despite performance indicators, simply because the voters are convinced by the challenger of a need for change. Nick Panagakis, a pollster, coined what he dubbed the incumbent rule in 1989—that any voter who claims to be undecided towards the end of the election will probably end up voting for the challenger.