How do the elections work?
All 435 seats in the lower chamber of the federal congress, the House of Representatives, are re-elected every two years. (There are no term limits, and incumbents are often returned, so there is substantial continuity in the membership). House seats are broadly proportional to population, so California has lots of seats but Montana only a few.
The upper chamber, the Senate, has 100 seats; two for each state, however populous. In every even-numbered year, roughly one-third of senators are elected for a six-year term. Legislation has to pass both chambers to become law. Senators have some additional responsibilities compared with their colleagues in the House; chiefly these have to do with confirming (or not) presidential appointments.
