A notable feature of congressional elections is that the incumbent typically wins their seat again in the next election. In 2016 incumbency re-election rates were 97 per cent for the House and 90 per cent for the Senate

There are several factors responsible for high incumbency re-election rates.

· Safe seats and gerrymandering The 'winner takes all' system has allowed a huge number of safe seats, where a candidate wins so convincingly that they are expected to keep the seat at the next election. An appropriate system of proportional representation would end this. However, this problem is made worse by gerrymandering — drawing electoral boundaries to favour a certain social group or party. This lets the dominant party draw district boundaries in their favour, at the expense of the opposition. Racial gerrymandering was common before the civil-rights era as many state boundaries are drawn up by the politicians elected at state level.

· Pork-barrel legislation This is when a member of Congress proposes an amendment to legislation that will bring benefits (especially financial ones, such as infrastructure projects or service provision) to a particular group. An amendment added by a politician to add expenditure to a bill that benefits their constituency is referred to as an 'earmark, which is often criticised for promoting unnecessary spending and contributing to the budget deficit. Even fiscal conservatives will engage in such proposals to improve their re-election chances. Some see pork-barrelling as evidence of the highly representative nature of Congress; others see it as a form of over-representation, in which financial benefits are not spread evenly around the country or constituency. In 2010 Republican leaders placed a moratorium on earmarks in order to restrict pork-barrel legislation, but this did not stop the practice altogether. In 2016, Congress passed legislation to spend $475 million on a new navy ship that the Defense Secretary and navy did not want, especially after a Pentagon report showing its unreliability. The project was supported by Representatives Byrne from Alaska and Ribble of Wisconsin, who represent districts with major shipbuilding companies.

· Financial advantage Incumbents can attract more money than challengers, allowing them to run more successful campaigns. Challengers can struggle to gain name recognition and often find themselves under attack through well-funded negative adverts.

High incumbency re-election rates can be seen as a threat to US democracy, suggesting an ineffective level of representation. Some states tried to resolve this by creating term limits for their Congressmen and Senators, but this was struck down by the Supreme Court. Term limits would end the stagnation of politicians in Congress, but they would only be attacking a symptom of incumbency. The major underlying causes, such as funding and gerrymandering, would remain, along with significant concerns about how representative members of Congress were.