Representatives only serve a two-year term before they must run for re-election. So, every time the calendar year ends in an even number, all 435 of the U.S. House members are up for reelection again.(Unless, of course, they choose not to run for reelection.).ll of them. Representatives only serve a two-year term before they must run for re-election. So, every time the calendar year ends in an even number, all 435 of the U.S. House members are up for reelection again. (Unless, of course, they choose not to run for reelection.).