http://www.washingtonmonthly.com/archives/individual/2006_07/009228.phpINCUMBENTS....When I was taking political science classes in the late 70s, the reelection rate for incumbents in the House of Representatives was upwards of 90%. This was seen as a worrying thing. Flash forward to today and most people would be delighted if the incumbent reelection rate were that low. In recent elections it's hovered around 98%. There are several reasons for this:
Gerrymandering has always been with us, but it's become easier and more precise in recent years. In the past, only a political genius could perform genuinely high-quality gerrymandering. Today it's available to anyone with a PC and the right software.
Conservatives and liberals have been showing an increasing tendency to self-segregate. That is, liberals tend to move to liberal places and conservatives tend to move to conservative places. This has an obvious self-gerrymandering effect, but also has the less obvious effect of making people more partisan. When you spend time only with people you agree with, your views tend to become more extreme. This is good for incumbents since extreme voters are less likely to defect to the opposition.
In a weird sort of vicious circle, Congress passes deliberately complex laws and then spends vast amounts of money on constituent services to help voters who are having trouble with federal bureaucracy. Because of this, constituent service has skyrocketed in the past few decades, and the beneficiaries of this service tend to vote for the people who helped them regardless of party affiliation or ideology.
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Due to rules, the last two items on the list are concentration of money/incumbent's ability to outspend challengers and fewer true independents now than in the past.
Also from 1999
http://www.cookpolitical.com/column/1999/033099.php During the first ten elections after the end of World War II, the Senate incumbent re-election percentage was all over the map, ranging from a low of 56.7 percent in 1946 to a high of 96.6 percent in 1960. The average for this period (1946-64) was 74 percent. (By comparison, the House incumbent re-election rate during the period ranged from 79.3 to 94.6 percent, averaging 89 percent. )
The unusually low re-election rate in 1946 was a manifestation of a devastating election for Democrats, one in which they lost 12 Senate and 45 House seats. Generally speaking, the incumbent re-election rates on both the House and Senate sides plummet when one party is getting pasted. In "normal years," when neither party is getting hammered, re-election rates remain relatively constant.
The next ten-election period, 1966-84, saw the Senate incumbent re-election percentage rise just two points to 76 percent -- ranging from 55.2 in the 1980 Reagan landslide to 93.3 percent in 1982. Interestingly, 1982 was a recession year and something of a downer for the GOP nationally. The party lost 26 seats in the House, but held its own in the Senate, just barely holding a number of seats by the narrowest of margins. (The House re-election rate increased three points during this period, to 92.6 percent.)
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Also
http://www.thisnation.com/question/016.htmlI read somewhere quite a while back that incumbents in the U.S. have a better chance of being returned to office than members of the old Soviet Politboro. I don't think that's a good thing.