How long is a term for a U.S. senator?

Why this is the answer

Senators are elected for six years, three times as long as a member of the House. The terms are staggered: the Constitution divides the Senate into three groups, so about a third of the seats come up for election every two years and the chamber never turns over all at once. The long term was meant to make the Senate a steadier body, less moved by the mood of the moment than the House. Memory hook: House 2, President 4, Senate 6.