Americans vote on 3 November for every House seat and about a third of the Senate. Here is the arithmetic, the historical record, and what forecasters and betting markets make of the four ways control of Congress could land — including what it would mean for impeachment.
A bill becomes law only if both chambers of Congress pass it, so control of each matters on its own. Republicans hold both today. The House has 218 Republicans, 214 Democrats, one independent and two empty seats.1 A majority is 218 of 435. Democrats won 215 seats in 2024,2 so they need to win three more seats than they lose — a “net gain” of three.3
The Senate splits 53 Republicans to 47 Democrats, a total that includes two independents who side with the Democrats.4 Under the Constitution the vice-president casts the deciding vote in a tie,5 and the vice-president is a Republican, JD Vance. Democrats therefore need 51 seats: a net gain of four.
The two hurdles are not alike. Every House seat is elected every two years, while senators serve six-year terms and only about a third face the voters in any one election.5 Which Senate seats are up is fixed in advance, so the map can matter as much as the national mood.
A midterm is the election held halfway through a president’s four-year term. Since 1946 there have been 20 of them, and the president’s party lost House seats in 18. The only gains came in 1998 and 2002. Across all 20, the average change was a loss of about 26 seats; the typical (median) loss was 22.2
The size of the loss varies widely, from four seats in 1986 to 64 in 2010. The American Presidency Project, a University of California archive, finds that presidents with lower approval ratings tend to lose more seats, and notes that only three presidents since 1936 went into a midterm with approval below 40%, the range Donald Trump is in now. Their parties lost 56, 28 and 30 House seats.8 That is a pattern, not a law: the archive’s own figures show the relationship is only moderately strong.
Pollsters ask a “generic ballot” question: which party would you back for Congress, without naming candidates. A New York Times/Siena College poll of 1,503 likely voters, taken 8–13 September, found 51% for Democrats and 43% for Republicans, with a margin of error of 2.9 points on each figure.9 The eight-point gap is wider than the error on the gap itself, roughly six points by our calculation, so it is unlikely to be a sampling fluke.
A national lead does not convert neatly into seats. Several states, including Texas and California, redrew their congressional maps mid-decade to help one party or the other.10 In the Senate, only the states on this year’s map count.
Each chamber goes to one party or the other, so there are four possible results. What each would mean follows from the Constitution’s rules.5
Democrats win both. Democrats would decide which bills get votes. Mr Trump could still veto legislation, and overturning a veto takes two-thirds of both chambers, far more seats than either party holds today. His nominees for judgeships and top posts would need a Senate that Democrats run.
Democrats win the House only. Because both chambers must pass a law, the House could block any bill. The House can also impeach — formally charge — an official by a simple majority, but removal needs two-thirds of the Senate. A Republican Senate would keep confirming nominees.
Republicans keep both. The current arrangement continues into the final two years of the term.
Democrats win the Senate only. Democrats would control confirmations while Republicans kept the House. Both sources below rate this the least likely outcome.
These are estimates of what might happen, not results. A forecast model run by Decision Desk HQ, an election-data firm, gives Democrats a 71% chance of the House and 53% of the Senate.11 On Polymarket, a betting market where prices act as odds, traders put the chance of a Democratic sweep at 66%.12
The two agree on the order: a Democratic House is the likeliest result, and a Democratic Senate with a Republican House the least likely. They disagree most on whether Republicans keep both chambers — about one chance in four for the model against about one in twelve for the market. Adding up the outcomes, the market gives Democrats roughly a 92% chance of the House, well above the model’s 71%.
On the Senate, the model rates two Republican-held seats as leaning Democratic — North Carolina (likely) and Alaska (lean) — and four more as toss-ups: Iowa, Maine, Ohio and Texas. It rates Michigan, a Democratic seat with no incumbent running, as leaning Democratic.11 On our reading of those ratings, the shortest Democratic route to 51 is to win North Carolina and Alaska, take two of the four toss-ups, and lose nothing they hold.
What it is. Impeachment is the House bringing formal charges against an official, much like an indictment in a court. The Constitution allows it for “Treason, Bribery, or other high Crimes and Misdemeanors”, and a simple House majority is enough. The Senate then holds a trial. Conviction needs two-thirds of the senators present; it removes the official from office, and the Senate may also bar them from holding office again.5
What it could be for. The articles filed in this Congress have come from individual Democrats, not party leaders. The latest, from Representative Al Green, accused Mr Trump of abusing his power over immigration enforcement. On 15 September the House set it aside by 232 votes to 147; 47 members, including the Democratic leadership, voted “present”.13 Hakeem Jeffries, the Democratic leader, says he has ruled nothing in or out, and that any case would start with committee investigations.14 The party has not agreed any charges.
How likely. Before the new Congress sits in January, very unlikely: the Republican-run House has set aside each attempt. Over the whole term, to January 2029, Polymarket traders price a 69% chance of impeachment — but it is thin, with about $100,000 traded against $13.5m on the market in Exhibit 02.15 On our reading, the question turns almost entirely on who wins the House.
What it would mean for Mr Trump. Impeachment alone would not remove him. He would become the first president impeached three times,16 but would stay in office unless two-thirds of the Senate voted to convict — which has never happened to a president (Exhibit 03). If Democrats won 51 to 53 Senate seats, 14 to 16 Republicans would have to join them; the most who have voted to convict Mr Trump is seven, in 2021.16 If he were removed, Vice-President Vance would become president.5 Mr Trump has told Republicans that losing the midterms would see him impeached.17
A growing number of Democrats say Mr Trump has already committed impeachable offences; Mr Green’s articles cited deaths at the hands of federal immigration agents.2013 Democratic leaders call impeachment the Constitution’s tool for holding a president to account for abuse of power and breaking the law.21
Republicans argue impeachment would overturn voters’ choice in 2024, making Mr Trump a “two-year president”. Some Democrats oppose it for a different reason: with conviction unlikely in the Senate, it could spend time and goodwill better used on voters’ everyday concerns.20
Which forecast is better calibrated. The model and the market use different methods and neither can be checked until November. A 26% outcome should happen about one time in four. In 2022 FiveThirtyEight’s final forecast gave Republicans a 59% chance of the Senate; Democrats held it.22 In 2018 its most likely outcome, a split Congress, did happen.23
What the new maps are worth. The three-seat figure is measured on 2024 results. With several states using redrawn districts, how many seats each party is really defending is an estimate, not a count.10
How much the mood moves. Six weeks remain. Polls and prices have shifted during the campaign and can shift again.