2026 US congressional midterm elections: Goldman Sachs relaunches its midterm tracker as markets favor Democratic control of the House and give Democrats an edge in the Senate

Overview

Goldman Sachs reintroduces its US Election Monitor to track the 2026 congressional midterms through polling, prediction markets, campaign-finance data and historical midterm comparisons. Its current read is favorable to Democrats, especially in the House, but it frames the Senate outlook as less settled because most pivotal polling margins remain within the margin of error.

Core views

The report’s starting point is that Democrats currently have a strong path to House control and a credible, though less certain, path to Senate control. Prediction markets imply more than a 90% probability that Democrats gain at least the three House seats needed for a majority. Democrats lead the national generic ballot by an average of 8.5 percentage points, versus the 2.6-point popular-vote margin won by House Republicans in 2024; Goldman Sachs interprets this as an approximately 11-point swing in national support. Republicans hold 26 seats in districts that President Trump carried by less than 11 percentage points, broadly the set of districts that markets and analysts expect to flip. The report expects mid-decade redistricting to add only a few Republican seats if current polling proves accurate, while prediction markets imply a greater than 50% chance that Democrats gain 24 seats—well beyond the three needed for a House majority. For the Senate, prediction markets imply more than a 60% chance that Democrats win the majority, which requires a net gain of four seats. Polling averages show Democrats ahead in six Republican-held seats and in their own close contests, although most leads are within the margin of error. North Carolina is widely expected by markets and expert ratings to move to Democrats, while Democrats also lead polls in five other Republican-held seats and are favored by markets in all but one of those. Texas has become the implied marginal Senate race, with prediction markets assigning roughly 60% odds of a Democratic win there. Goldman Sachs notes that convergence between the overall Senate-control odds and the odds of winning the marginal Democratic seat may signal more perceived paths to a majority, higher correlation across races, or both. The report identifies recent momentum behind the Democratic position. National generic-ballot margins have reached cycle highs, with the average Democratic advantage up 2 percentage points since the start of September. It also notes that the Democratic generic-ballot lead widened gradually after the gasoline-price spike at the onset of the Iran war, and that the two series have recently moved in the same direction. Inflation and the economy rank as voters’ most important issues, while President Trump’s net approval on both is deeply negative. Markets averaging Kalshi and Polymarket odds now price more than a 60% chance of a Democratic sweep of both chambers and less than a 10% chance that Republicans retain the House majority. Goldman Sachs nevertheless highlights financing and measurement risks to the current polling picture. Republican organizations have begun spending heavily in pivotal Senate races, widening an already sizable Republican cash advantage. Republicans have outspent Democrats in most key Senate races; Democrats have outspent Republicans only in Georgia, Kansas and South Carolina. Republicans began cumulatively outspending Democrats in key Senate contests only in September, so current polling may not yet reflect the full effect. In House races, aggregate Democratic spending is stronger, but Republicans lead most head-to-head matchups. The report cautions that the House spending data exclude estimated advertising over the next two months, which has skewed heavily Republican, and that candidate spending and cash-on-hand data are lagged by quarterly disclosure. Finally, the report tests current signals against historical midterm patterns. It finds that prediction-market odds of a sweep by the challenging party have, on average, declined as Election Day approaches. It also finds that at this stage of recent midterm cycles, Senate polls have on balance overstated Democratic performance. State-level evidence suggests polls tend to understate Democrats in Democratic-leaning states and Republicans in Republican-leaning states, consistent with late-cycle voters returning to their party; if that pattern repeats, Democratic leads in Republican-leaning Senate contests could overstate their actual position. These caveats explain why the report presents the House outlook as much firmer than the Senate outlook despite currently favorable Democratic indicators.

Analysis framework

The report combines national and state polling averages, prediction-market probabilities, Cook Political Report race ratings, historical election and polling-error comparisons, and Federal Election Commission spending data. It compares current national vote conditions with 2024 district margins, then tests whether current market and polling signals may be distorted by late-cycle spending or recurring midterm polling patterns.

Methodology notes

• Other

  Prediction-market probability tracking

  The report uses market-implied odds from Kalshi, Polymarket and other platforms to gauge the probabilities of chamber control, individual race outcomes and a Democratic sweep.

• Other

  Historical polling-error comparison

  The report compares polls at a similar point in prior midterm cycles with realized results to assess whether current Democratic polling leads may be overstated.

Key data

• Democratic probability of Senate majorityMore than 60%Prediction-market estimate; Democrats need a net gain of four seats.
• Democratic probability of gaining House majorityMore than 90%Prediction markets imply Democrats will gain at least the three seats required.
• Democratic generic-ballot lead8.5ppImplies roughly an 11pp swing from the 2.6pp House popular-vote margin won by Republicans in 2024.
• Republican-held House seats in Trump districts under 11pp26These are generally the districts markets and analysts expect Democrats to flip.
• Probability of Democratic sweepMore than 60%Based on averaged Kalshi and Polymarket odds.
• Probability Republicans retain House majorityLess than 10%Current prediction-market pricing.
• Change in Democratic generic-ballot advantage since early September2ppThe national margin widened to cycle highs.

Impact & implications

The report’s data point to a Democratic-favorable midterm environment, with the House outcome appearing more strongly supported by markets and the generic ballot than the Senate outcome. Its principal qualification is that campaign spending and historical polling bias could erode the apparent Democratic Senate advantage as the election approaches.

Risks

• Most key Senate polling margins are within the margin of error.
• Historical evidence suggests polls at this point in a midterm cycle have tended to overstate Democratic Senate performance.
• Republican spending and fundraising advantages may not yet be fully reflected in polling.
• House spending data exclude estimated advertising over the next two months, which has been heavily Republican, while candidate-finance data are lagged.

What to watch

• Whether Democratic generic-ballot margins remain at cycle highs or reverse.
• Polling and prediction-market movement in Texas, the implied marginal Senate race, and in New Hampshire, Kansas and South Carolina.
• The effect of recently increased Republican spending in competitive Senate and House races.
• Whether historical late-cycle declines in challenging-party sweep odds and polling-error patterns reappear.