Traders Flip Senate Control Bet as Democrats Overtake Republicans on Kalshi, Polymarket

In brief

• Contracts on Kalshi and Polymarket now give Democrats a 51% chance of winning Senate control, edging Republicans at 49%.
• The shift marks a dramatic reversal from a year ago, when markets priced Democrats at just 18% probability of taking the chamber.
• Kalshi data shows Democrats’ odds have risen 11 percentage points since U.S. military involvement in Iran began about two weeks ago.

Prediction markets have shifted to favor Democrats to control the U.S. Senate after the 2026 midterm election, marking the first time the party has taken the lead in the race’s history on platforms tracking the outcome. Contracts on prediction platforms, including Kalshi and Polymarket, show Democrats with a roughly 51% chance of winning Senate control, compared with 49% for Republicans, as of late Friday.  On Myriad Markets, owned by Decrypt’s parent company Dastan, traders are pricing the chances of Democrats sweeping the 2026 midterms at about 50-50.

“The Democratic Party is now favored to win the Senate for the first time in the race’s history,” said Jack Such, a Kalshi spokesperson, wrote to Decrypt. “The race is now essentially a coin flip, with Democrats having a 51% chance to win.”  The narrow lead represents a dramatic reversal from a year ago, when markets priced Democrats at just 18% probability. The shift reflects a steady repricing by traders over recent months that accelerated in the past few weeks amid escalating geopolitical tensions between the U.S. and Iran.

It also comes as a surprise because the Senate had long been expected to remain in Republican hands. While they are widely expected to face a difficult fight to hold the House after the midterms, the Senate map had been viewed as structurally favorable to President Donald Trump’s party. Prediction markets allow traders to buy and sell contracts tied to real-world outcomes, with prices reflecting participants’ collective expectations. They’ve often been used to correctly predict political outcomes, including the 2024 Presidential Election, which tipped a Trump victory. According to Kalshi data shared by Such, the turnaround has been particularly sharp in the past two weeks. Since the start of American military involvement in Iran roughly 16 days ago, the Democrats’ implied probability of controlling the Senate has increased by about 11 percentage points, he said. The move suggests traders may be reassessing how geopolitical developments could influence U.S. politics heading into the next election cycle. While the 2026 midterms remain months away, prediction markets often react quickly to shifts in political sentiment, economic conditions and global events. Trading volumes on the markets remain relatively modest compared with traditional financial markets, though activity has increased as the race has tightened. Kalshi’s Senate control contract has generated more than $2.3 million in trading volume, while the equivalent market on Polymarket has seen close to $900,000 traded. With the contracts now pricing the race as effectively even, traders appear to be bracing for a volatile political cycle in which small changes in polling, policy, or global developments could swing the balance of power in the chamber.