Prediction markets have updated the probability of a Democratic sweep in the 2026 midterms to 61%, reflecting growing confidence among traders. Sen. Elizabeth Warren (D-Mass.) declared on Sunday that Democrats will win in November, citing grassroots momentum despite record dark money spending.

The odds on Polymarket rose from 49% a month ago, indicating a shift in market sentiment toward the blue party. Warren’s optimism follows the primary election success of progressive candidates, including Abdul El-Sayed in Michigan.

Prediction Markets Shift Ahead of 2026 Midterms

Polymarket traders currently assign a 91% chance for Democrats to take control of the House and a 61% chance for the Senate. This represents a significant increase from the 49% probability recorded just one month prior. The platform has seen sustained trading activity as Election Day approaches on Nov. 3.

While Republicans currently hold both chambers, the scenario where Democrats win the Senate but Republicans retain the House remains unlikely. The previous data point from Sept. 1 showed a 60% probability for a sweep, driven by declining support for President Donald Trump on inflation.

Dark Money and Grassroots Mobilization

Approximately $1 billion in anonymous funds has influenced or is expected to influence every major primary and battleground race in 2026, according to a New York Times analysis. Warren highlighted that dark money groups have spent record sums this year, targeting groups tied to AI, cryptocurrency, and the American Israel Public Affairs Committee.

Despite this financial pressure, Warren pointed to grassroots victories as evidence of voter engagement. Abdul El-Sayed won Michigan’s Senate primary by narrowly defeating Rep. Haley Stevens (D-MI) by less than one percentage point. El-Sayed’s campaign reportedly drove record turnout, overcoming more than $60 million in opposition spending with a 12,000-strong volunteer network.

Economic Factors and Voter Sentiment

President Trump’s approval rating on inflation has fallen to 19%, marking a new low in the latest Marquette Law School poll. CNN chief data analyst Harry Enten described the resulting minus-61 net rating as the worst presidential inflation reading on record. A Cato Institute/Morning Consult survey found that 75% of registered voters say tariffs will influence their midterm vote.

Among voters citing tariffs as a voting factor, 55% plan to back Democratic congressional candidates compared to 36% for Republicans. Marquette now gives Democrats an 11-point advantage on handling inflation and the cost of living, a sharp reversal from October 2024 when voters trusted Trump over Kamala Harris by seven points.

Fed Rate Hike and Market Reaction

The political shift coincides with the Federal Reserve raising rates by 25 basis points to 3.75%-4%, its first hike since 2023. Sixteen of 18 policymakers expect at least one more increase this year. Polymarket traders assigned an 81% probability to at least one additional hike.

Equity markets reacted to the rate decision with initial declines followed by recovery. The S&P 500 fell 0.44% Wednesday before rising about 1.1% Thursday as Treasury yields and oil prices eased. The tech-heavy Nasdaq Composite finished nearly flat Wednesday before rising about 1.6% Thursday.

What the Numbers Show

The divergence between partisan loyalty and economic perception is stark. While Republicans maintain a net approval of minus 4 on inflation—significantly better than Democrats’ minus 95—the broader electorate has shifted decisively. The 11-point Democratic advantage on inflation handling, combined with the 61% prediction market pricing for a full Democratic sweep, suggests that tariff-induced price pressures are outweighing traditional base support in voter decision-making.