Incumbency

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).

...
Wikipedia