The US has a census every 10 years and the 435 seats in the House of Representatives are apportioned to reflect the population change. Sometimes states lose seats. New York state had 45 seats in the 1940's and has lost between 2 and 5 seats for every subsequent census.
What happens to the representatives for those districts that are lost?
I understand that representatives have to campaign for their reelection every two years, including both primaries and the general election. Even so, after a census the party members need to decide which of their representatives campaign for which newly-formed congressional districts and which get booted out. Do they typically do this through gentleman's agreements, primary contests or some other means?