Prediction markets favor Democrats to win both chambers of Congress

Prediction markets imply a Democratic sweep of Congress in today's US midterm elections. The chance of Democrats winning the Senate has climbed sharply in recent weeks.

Kalshi and Polymarket quotes as of roughly 8 am ET on Tuesday, November 3, showed:

• House: Democratic chance 94–95%, Republican chance 6–7%

• Senate: Democratic chance 78%, Republican chance 23–24%

The largest shift has come in the Senate contest. Kalshi priced Democratic control at 74% at midday Monday, compared with 63% in early October and 44% in March.

Kansas would be the biggest surprise. It is the seat formerly held by Mitch McConnell, who last won it in 2020 by 57.76% to 38.23%. The odds turned around only in the past week.

I am doubtful about that one, though Republicans have had some dreadful polls lately. Still, this script has played out before: some pollsters declared Trumpism finished just before the 2024 election, and he then won big.

Among other notable races, Democrat Roy Cooper is priced at 97% in North Carolina, while Democratic incumbent Jon Ossoff is at 96% in Georgia.

Republicans currently hold a 53–47 Senate majority, so Democrats need a net gain of four seats to secure outright control. As a cross-check, UK bookmakers give Democrats roughly 75-78% odds of controlling the Senate, close to the same level.

The House market is far more one-sided: Democrats are trading near 95% to regain control.

For the Senate, Nate Silver's model assigns Democrats an 82% chance, and 96% for the House. Poliwave's figure for the Senate is 85%.

The first meaningful signals are due around 7:15–8:00 pm ET tonight, and a much clearer picture should emerge by 9–10 pm. Kentucky, Virginia, Georgia, North Carolina and Ohio are the earliest races to watch.

Two things are worth watching: how the Democratic margin in early-reporting House districts compares with the 2024 presidential election, and whether Republicans beat or fall short of expectations in the Senate races.