Warren and Curtis Press Kalshi and Polymarket on Election Insider Trading

Two senators, one from each party, have asked the two largest US prediction markets to show how they keep insiders and manipulators out of election contracts, with answers due on the day of the midterms. The letter argues that catching a handful of candidates is not proof the markets are protected.

• Senators Elizabeth Warren, a Massachusetts Democrat, and John Curtis, a Utah Republican, wrote on 28 October to Kalshi chief executive Tarek Mansour and Polymarket chief executive Shayne Coplan about election event contracts
• The letter asks how each platform stops candidates, campaign staff, election officials, pollsters and others with nonpublic information from trading, and how many suspected cases it has found and referred to the Commodity Futures Trading Commission (CFTC)
• Written answers were requested by 3 November, the day of the midterm elections, according to reports of the letter
• It cites Kalshi candidates who traded on their own races and a 2024 estimate that about a third of volume on Polymarket's presidential market was wash trading
• Kalshi says it blocks candidates and campaign staff, while Polymarket has published no response, and the letter adds to pressure from Utah prosecutors and Senator Richard Blumenthal

Two Senators Ask the Exchanges to Prove Their Election Markets Are Clean

Senators Elizabeth Warren (D-Mass.) and John Curtis (R-Utah) sent a joint letter dated 28 October to the heads of Kalshi and Polymarket, according to The Hill, which reported it on 29 October. The senators wrote that they were "particularly troubled by election-related event contracts" tied to the 3 November midterms, according to Bitcoin.com News, and asked for written answers by Election Day.

The letter sets out seven questions, according to Bitcoin.com News, covering how each company keeps insiders such as candidates, campaign staff, election officials and pollsters from trading, including through third parties or affiliated accounts, and how it detects wash trading. The senators also ask how many suspected insider trading or manipulation cases in election contracts each platform has identified since 1 January, how many were stopped before a trade executed rather than found afterwards, and how many were referred to the CFTC or law enforcement. Another asks whether surveillance has been independently evaluated, and The Hill reported a question on what each company does beyond checking Federal Election Commission filings.

The Cases the Letter Relies On

For Kalshi, the letter points to candidates who bet on their own races in 2025 and in April 2026, according to reports. Those cases "raise critical questions about how many election-related transactions have escaped detection", the senators wrote, as quoted by Yogonet and Bitcoin.com News. Kalshi said on 6 October that it had fined and suspended four congressional candidates in 2026 for trading on their own races.

For Polymarket, the letter cites a Fortune report from 30 October 2024. In it, the analytics firm Chaos Labs estimated that around a third of trading volume on Polymarket's presidential market was wash trading. A second firm, Inca Digital, gave no figure.

Kalshi's head of enforcement, Robert DeNault, told The Hill that "Kalshi prohibits insider trading and market manipulation and proactively blocks candidates and campaign staff from trading." In an October newsletter, Kalshi said it bans anyone who can influence an election outcome, from members of Congress to poll workers, and verifies every account's identity. Polymarket did not immediately respond to The Hill, and had not published a response to the letter.

A Bipartisan Signature Changes the Politics

Warren has long opposed election and sports contracts. Curtis's signature is the news, and his state matters. Utah prosecutors have filed criminal charges against Kalshi's founders, and the CFTC has sued Utah over that case. That makes the scrutiny harder to dismiss as partisan. It is still a letter from two senators, not a Senate inquiry, and it carries no power to compel answers.

The Regulator Has Stepped Back From the Question

On 4 February the CFTC withdrew its June 2024 proposed rule on event contracts, which Chairman Michael Selig described as "an outright prohibition on political contracts", and said it did not intend to finalise it. That leaves surveillance of election markets largely to the exchanges' own rulebooks and referrals. The letter's questions on cases caught before a trade, and on referrals to the CFTC, test that arrangement. Election officials have moved to bar poll workers from trading, and the Pentagon has barred staff from trading on nonpublic information, so other institutions are not waiting for the exchanges.

Thin Markets Make the Manipulation Question Concrete

The Anti-Corruption Data Collective (ACDC) found that a $3,500 bet could move 97% of midterm-related markets by five cents or more, CNBC reported on 9 September. Kalshi called the method flawed, saying liquid markets correct mispricings quickly. The same group counted more than $220 million bet on this cycle's congressional races through 30 September, against $92 million for the whole 2024 cycle, according to Reuters. Volume spread across more than 21,000 markets, the group's count, is the condition in which a few wallets can move a price.

Whether either company answers in detail, and whether the senators publish what they receive, will show how much of this surveillance can be checked from outside. Until then, the public record on election-market integrity rests largely on what the exchanges choose to disclose.