Although Rep. John Dingell of Michigan's 57 years, five months and 27 days and counting as of June 7, 2013, is a record for serving in Congress, almost all incumbents do have an election advantage in both the House of Representatives and the Senate.

Favored Candidates

Simply because they've been elected before, incumbents have an edge. Generally, citizens liked them enough to vote for them previously, and, unless something drastic has happened, those positive feelings haven’t changed. To win in the first place, candidates had to pass muster with constituents. This is especially important during years when there isn’t a presidential election. During these elections, much of the voter turnout consists of party loyalists and activists.

Lack of Competition

It can be difficult to find a candidate to stage an uphill battle against a sitting member of Congress. Researchers from Washington University, the University of Iowa and the University of Minnesota looked at the quality of candidates in Senate elections with open seats – no incumbent was running -- and compared them to candidates fighting an incumbent. The open-election candidates were more qualified for the positions.

New Boundaries

The process of redistricting, which occurs every decade after the census determines population, can have a serious effect on elections. When state legislatures draw new districts, the party in power within the state can ensure that many areas are “safe” for its congressional candidates, including incumbents. However, incumbents from the minority party may find themselves in totally new districts, with their bases of support virtually eliminated. In some cases, incumbents have been pitted against each other.

Money

With changes in campaign finance laws, much of the big money for political campaigns comes from corporations, unions, political action committees and lobbyists. Their money goes to proven entities: incumbents who have a say in lawmaking and have already cast favorable votes. New candidates have no legislative power before the election, and interest groups don't know if novice congresspeople will support them.

Members of Congress can spend much of their time fundraising. However, new candidates are usually working full-time, so they have less opportunity to focus on donors. In addition, incumbents are often able to get popular politicians to host or participate in fundraisers.

Exposure

Incumbents can be in the public eye continually, sending mailings, holding town hall meetings and speaking to the media. They can advertise what they've done for their districts: introducing or voting for favorable legislation and obtaining federal money. Incumbents can also get positive publicity and feelings of good will by helping individuals with government problems.