The first polling stations have opened in Vermont, starting at 5am (10:00 GMT). Voting in New Jersey, Virginia, Connecticut, and parts of Kentucky and Indiana started an hour later. The Department of Justice on Tuesday announced the deployment of a record 1,000 election monitors across all 50 US states.

All 435 House of Representatives seats and 35 of the Senate’s 100 seats are up for grabs. Voters in 36 states will also elect governors.

If Democrats win control of Congress, they could stall Trump’s legislative agenda. About 58 million of 210 million registered voters have already cast their ballots through early in-person and mail-in voting.

The first results are expected on Tuesday as polls begin to close at 23:00 GMT. But final results might take days.