Americans head to the polls on Tuesday 3 November for midterm elections that will decide control of Congress, with all 435 House seats and a series of Senate races on the ballot. President Donald Trump is not himself on the ballot, but the results will shape how much of his agenda can pass in the remaining two years of his term, since Republicans currently control both chambers.

National polling points to a Democratic advantage in the House race, though polls are snapshots of voter preference, not results. An NBC News polling average recently put voters preferring Democratic control of the House at 52% against 43% for Republicans, while Call the Map had Democrats ahead by 7.7 points on the generic congressional ballot and another weighted average, POLLSMAX, put them at 50.9% to 42.8%. Forecasters give Democrats a strong chance of taking the House, where 218 seats are needed for a majority, but describe the Senate as much closer, with Democrats needing a net gain of four seats for an outright majority.

Divided government is the likeliest outcome

Analysts at JP Morgan Asset Management assess divided government as the most probable result, with at least one chamber changing hands, while noting that even a Democratic sweep would be unlikely to produce majorities large enough to override a presidential veto, which requires two-thirds in both chambers, or to overcome a Senate filibuster, which requires 60 votes. History also favours the party out of the White House: the president's party has lost ground in the House in 20 of the past 23 midterms, by an average of 27 seats. Affordability, fuel and mortgage costs, and the Middle East conflict's effect on prices are all cited as factors weighing on Republican support.