By laws of the U.S. Constitution, the federal government is required to carry on a census every 10 years that calculates how many people are currently living in each state. Occasionally, as the population goes up or down in certain states, a reapportionment of U.S. House seats must be done in order to adjust to the changes.
Re-election rates for incumbent members of the congress has always been extremely high. Historically, it has rarely gone down 90%. However, for States that experience slow growth or rapid loss of population, the threat of losing seats becomes an actual concern for congress members.
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