How do US midterm elections work?

The United States holds federal elections every two years, on the Tuesday after the first Monday in November. Every fourth year, the president is elected. The elections in between are called midterms.

Congress has two chambers. The House of Representatives has 435 members, each representing a district of roughly equal population, elected for two-year terms. So every House seat is on the ballot at every midterm.

The Senate has 100 members, two for each state, elected for six-year terms. Terms are staggered, so about a third of seats are contested every two years. Special elections fill seats that have become vacant.

Most states also elect governors, state legislators and local officials, and many hold votes on ballot measures, proposed state laws chosen directly by voters.

Control of Congress matters because both chambers must pass a bill before it becomes law, and the Senate confirms judges and senior officials. When the president's party loses control of one chamber, it becomes harder to pass laws.

Each state runs its own elections, with its own rules on early voting and postal ballots. Counting can take days in close races, and results are certified by the states weeks later.