Warren and Curtis Demand Answers from Kalshi and Polymarket on Election Trades

Two US senators sent a joint letter on 28 October asking the two largest US prediction markets to explain how they prevent insider trading and manipulation in election-related contracts, with written answers requested by 3 November, the day of the midterm elections. Senators Elizabeth Warren, a Massachusetts Democrat, and John Curtis, a Utah Republican, addressed the letter to Kalshi chief executive Tarek Mansour and Polymarket chief executive Shayne Coplan and set out seven detailed questions about surveillance and referrals to regulators.

What the senators asked for

The 28 October letter asks each platform to explain how it prevents trading by candidates, campaign staff, election officials, pollsters and others with nonpublic information, including through third parties or affiliated accounts. It requests numbers of suspected insider trading or manipulation cases in election contracts identified since 1 January, how many were stopped before execution rather than detected afterwards, and how many were referred to the Commodity Futures Trading Commission (CFTC) or law enforcement. The senators also asked whether each platform's surveillance has been independently evaluated and what the companies do beyond checking Federal Election Commission filings.

The letter's seven questions, as summarised in reporting from Bitcoin.com News and The Hill, put particular weight on detection before execution and on formal referrals to the CFTC.

Cases cited in the letter

For Kalshi, the letter points to candidates who traded on their own races in 2025 and in April 2026. Kalshi publicly said on 6 October that it had fined and suspended four congressional candidates in 2026 for trading on their own races. 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." Kalshi also said in an October newsletter that it bans anyone who can influence an election outcome, from members of Congress to poll workers, and verifies every account's identity.

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

Polymarket had not published a response to the senators' letter at the time reporting captured the correspondence. Reports noted that Polymarket "did not immediately respond to The Hill."

Broader pressure and regulatory context

The letter arrives amid other scrutiny of election markets. Utah prosecutors have filed criminal charges against Kalshi's founders, and the CFTC has sued the state of Utah over that case, making cross-party scrutiny harder to dismiss as purely partisan. The letter is a Senate correspondence rather than a formal Senate inquiry and therefore has no subpoena power.

The Commodity Futures Trading Commission withdrew a June 2024 proposed rule on event contracts on 4 February 2026. CFTC Chairman Michael Selig described the proposal as "an outright prohibition on political contracts" when the agency said it did not intend to finalise the rule. That withdrawal leaves surveillance of election markets largely to exchange rulebooks and to referrals to the regulator.

Other institutions have taken steps independent of the platforms. Election officials have moved to bar poll workers from trading, and the Pentagon has barred staff from trading on nonpublic information.

Liquidity, market thickness and manipulation risk

The Anti-Corruption Data Collective (ACDC) produced analysis showing that a $3,500 bet could move 97% of midterm-related markets by five cents or more, a figure CNBC reported on 9 September. Kalshi responded to ACDC's methodology by calling it flawed and arguing that more liquid markets correct mispricings quickly. ACDC also counted more than $220 million bet on this cycle's congressional races through 30 September, compared with $92 million for the whole 2024 cycle, Reuters reported. The group said volume is spread across more than 21,000 markets, a condition in which a small number of wallets can move a price.

Those liquidity figures and the Chaos Labs estimate on Polymarket are the quantitative anchors the senators cite to press exchanges to show how many suspected manipulations escape detection.

What happens next

The senators requested written answers by 3 November. Whether Kalshi and Polymarket provide detailed responses, whether the senators publish what they receive, and whether the CFTC or law enforcement receive new referrals will determine how much of election-market surveillance can be verified from outside the platforms. Until those documents are published, the public record on election-market integrity relies mainly on exchange disclosures, the 6 October statement from Kalshi, the Fortune reporting of 2024, the ACDC liquidity analysis and the CFTC's 4 February 2026 withdrawal of the event contracts proposal.

"Kalshi prohibits insider trading and market manipulation and proactively blocks candidates and campaign staff from trading," said Robert DeNault, Kalshi's head of enforcement, to The Hill.

Kalshi's October newsletter and its public statement on 6 October are listed in reporting as primary company materials addressing these concerns. Polymarket had not issued a public reply to the October 28 letter at the time coverage was captured.