What do betting markets say about control of Congress?

Betting markets favor Republicans to control the Senate, but view the House as a toss-up

Election Day is less than a week away and voters are already heading to the polls and mailing in their ballots, and betting markets have weighed in on whether Republicans or Democrats are favored to win control of Congress.

Control of both the House of Representatives and Senate have been closely contested in recent years, with the last two Congresses having historically thin majorities in both the House and Senate. The GOP controlled a narrow 222-213 majority in the House at the outset of the current 118th Congress, after Democrats began the prior Congress with a majority of the same margin.

In the Senate, Democrats currently have a 51-49 majority when including independent senators who caucus with the Democratic Party. During the previous Congress, the Senate had a 50-50 split with Democrats controlling the majority by virtue of Vice President Kamala Harris' tiebreaking vote.

Traders on Polymarket see the trend of relatively narrow majorities continuing in the next Congress after this election. While the platform currently sees an 83% chance of a GOP majority in the Senate, bettors are also anticipating that it will be by a relatively small margin.

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Election Day polling place

American voters will determine the balance of power in Congress this election as Republicans and Democrats compete for majorities. (Michael Gonzalez/Getty Images / Getty Images)

Since early September, Polymarket traders have seen a 52-seat GOP majority as the likeliest outcome, which peaked at a 52% chance in early October but has since ebbed to a 25% chance. A slightly smaller 51-seat GOP majority is the next most likely outcome according to Polymarket bettors, with a 16% chance.

Bettors see an 11% chance that Republicans will end up with 49 or fewer Senate seats — which would give Democrats a narrow majority. They also see a 9% chance of a 50-50 bipartisan split, which would give the majority to the party that wins the White House and has a vice president who can cast tiebreaking votes in the Senate.

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Speaker Mike Johnson

House Speaker Mike Johnson, R-La., is hoping Republicans hold their House majority. (Eva Marie Uzcategui/Bloomberg via Getty Images / Getty Images)

Polymarket's traders see the battle for control of the House of Representatives as a virtual toss-up, with House Democrats having a roughly 50% chance of winning a majority over the past week. 

However, a separate market on the platform suggests that House Republicans are more likely to attain a larger majority than what has occurred in recent years, as it sees a 29% chance there will be 230 or more GOP seats in the House in the next Congress. It also shows a 15% chance the GOP ends up with fewer than 200 seats — which would leave Democrats with a majority of more than 235 seats.

BetUS' odds see control of the House of Representatives as a toss-up with Democrats and Republicans having equal odds. It also has Republicans as the heavy favorites to win control of the Senate. 

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Hakeem Jeffries and Chuck Schumer

House Minority Leader Hakeem Jeffries, D-N.Y., (left) and Senate Majority Leader Chuck Schumer, D-N.Y., are hoping to get Democratic majorities in both chambers of Congress. (Roberto Schmidt/Getty Images / Getty Images)

Control of both chambers of Congress and the presidency — known as a "trifecta" — has occurred in the first two years of the last three presidential administrations before the party in power lost control of one or both chambers in the midterm elections.

Trifectas are useful for enacting tax and spending policies using the budget reconciliation process, which allows budget-related legislation to pass through Congress on simple majority votes without being subject to the Senate's 60-vote threshold to overcome the legislative filibuster.

Polymarket traders see a roughly 46% chance of Republicans achieving a trifecta, with former President Trump winning alongside GOP majorities in the House and Senate. By comparison, the market sees a 15% chance of a Democratic trifecta following a victory by Harris and congressional Democrats. 

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Bettors on the platform see a 20% chance of a Democratic president and House with a GOP Senate, compared to a 16% chance of Republicans winning the presidency and Senate with Democrats controlling the House. 

Only one other outcome — Democrats winning the presidency and Republicans controlling both chambers of Congress — garnered a 5% chance in the market.