Sens. Elizabeth Warren (D-Mass.) and John Curtis (R-Utah) have pressed prediction market platforms Kalshi and Polymarket to detail their safeguards against insider trading and manipulation in election contracts. The bipartisan letter, released Thursday, gives both companies until Nov. 3 to answer seven questions about their oversight practices.
The senators expressed concern about election-related event contracts, which receive significant public attention and are sometimes viewed as indicators of political momentum. "We are particularly troubled by election-related event contracts," the letter states.
Questions on Surveillance and Detection
The seven questions ask how each company prevents candidates, campaign staff, election officials, pollsters, and others with nonpublic information from trading on election contracts. The senators also want to know how platforms stop such individuals from circumventing trading bans through third parties or affiliated accounts.
Additional questions address detection of wash trading and other manipulation, the number of suspected cases identified since Jan. 1, how many violations were stopped before execution, and whether the companies have referred cases to the Commodity Futures Trading Commission (CFTC) or law enforcement.
Documented Violations Cited
The letter points to specific incidents on Kalshi where candidates traded on their own races. According to a CFTC advisory from February, social media videos appeared to show a candidate trading on a contract tied to his own candidacy in May 2025. Kalshi fined the candidate and suspended him for five years. The company disclosed three additional such cases in April.
On Polymarket, the letter cites a 2024 Fortune report estimating that roughly one-third of the presidential election market's trading volume was likely affected by wash trading. The senators also referenced a recent Wired report identifying more than $600 million in trading on Polymarket election contracts involving Ethiopia and Romania, noting that trading continued in the Ethiopian market for months after the election concluded.
Company Responses
Kalshi's Head of Enforcement Robert DeNault told The Hill that the company "proactively blocks candidates and campaign staff from trading to protect market integrity." According to Kalshi, the platform uses Federal Election Commission payroll data to prevent such trading and has established an independent market integrity committee.
Polymarket has investigated dozens of bets tied to recent elections, with at least two cases referred to the CFTC, according to reporting. The company is also reviewing newly created wallets that placed bets on Benjamin Netanyahu shortly before Israel's election polls closed.
The senators emphasized that isolated instances of improper trading do not demonstrate adequate market protections, stating they remain skeptical about the companies' ability to effectively police these contracts.
