Probability of Democrats winning the House rises to 93%, is the Republican defeat in the midterm elections already certain?

According to PolyBeats monitoring, on the prediction market Polymarket, the probability of the Democrats winning control of the House in 2026 has risen to 93%. This probability was only about 57% in October 2025, and has continued to climb since then; this month it rose about 6 percentage points from a low of about 86.5%.

The market's relatively strong consensus stems first from the long-standing incumbent party penalty effect in U.S. midterm elections. Of the 22 midterm elections since 1938, the president's party lost House seats in 20 of them, with only 1998 and 2002 as exceptions. The current ruling party (Republican Party) has only a thin advantage (220 seats to 215 seats), and Democrats need a net gain of just 3 seats to reach the 218-seat majority threshold.

As a Democratic victory gradually becomes the market's mainstream expectation, betting on this topic in prediction markets has now become a "short-term high-yield product" for some traders: buy "Democrats win the 2026 House" at $0.93, and after the midterm elections end, $1 can be collected; calculated from September 30, if the market settles quickly after the November 3 election, holding for about 34 days corresponds to a simple annualized yield of about 80.8%.

scottilicious bought $244.27k of "Yes" at a purchase probability of 84.25%. This trader has made a total of 999 trades in the politics sector, with an 86% win rate and PnL +$1.1m. This investment is 27.92 times their median investment.

It should be noted that this annualized figure is only a time-based conversion under the premise that "Democrats win and settlement is timely." If settlement occurs only by November 15, the simple annualized rate is about 59.7%; if it is delayed until around January 4, 2027, due to runoff elections, independent lawmakers' caucus affiliation, and other issues, it drops to about 28.6%. More importantly, it is not a true fixed-income product. If Republicans unexpectedly hold the House, this position will go to zero.