Two senators from opposite parties gave Kalshi and Polymarket until Election Day to explain how they stop insider trading on the midterms

Analysis · Updated October 30, 2026 · 18+ · Not legal advice · By BetG8 Editorial · Prediction Markets

Warren and Curtis letter to Kalshi and Polymarket on election insider trading — The senators asked for answers by November 3, Election Day.

Short version: On October 28, 2026 Senators Elizabeth Warren (D-Mass.) and John Curtis (R-Utah) asked Kalshi and Polymarket to explain, by November 3, how they prevent insider trading and manipulation in midterm election contracts and which cases they have referred to the CFTC. The letter has no legal force and changes nothing for users before the vote, but it arrives in the busiest month either exchange has recorded and on the same day Utah charged Kalshi’s founders.

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What the letter asks

On October 28, 2026 Senator Elizabeth Warren, the Massachusetts Democrat who is ranking member of the Senate Banking Committee, and Senator John Curtis, a Utah Republican, wrote to Kalshi chief executive Tarek Mansour and Polymarket chief executive Shayne Coplan. The committee’s minority staff published the letter on October 29. It asks each company to explain what it does to prevent insider trading, market manipulation and trades placed on material nonpublic information in contracts tied to the November 3 midterm elections, and it asks for the answers by Election Day itself.

According to the Senate Banking release and reporting by The Hill, the questions cover four areas: the safeguards each exchange has in place now; what it does to stop campaigns and “other individuals with access to material nonpublic information” from trading, beyond screening names against Federal Election Commission filings; which cases of election-related insider trading it has referred to the Commodity Futures Trading Commission; and how it detects manipulation.

The letter has no legal force. A senator’s letter cannot compel a private company to answer, and neither company is required to change anything because of it. What it does is put both exchanges on record, in writing, five days before the largest election-market event since 2024.

The evidence the senators cite

The letter leans on three episodes. First, candidates who traded contracts on their own races on Kalshi, which the senators date to 2025 and April 2026. Second, alleged volume manipulation on Polymarket’s 2024 presidential market, which the letter, citing a Fortune report, puts at roughly one third of that market’s trading volume. Third, an NPR investigation into campaign insiders who traded ahead of the release of internal polling; NPR said it verified at least one such trade against prediction-market records.

The core of the argument is in one sentence the release quotes: “the identification of isolated instances of improper trading does not demonstrate that these markets are adequately protected. Instead, it raises serious questions about how much similar activity may be going undetected.” In other words, the senators read Kalshi’s publicised enforcement cases as evidence of a problem, not as evidence that surveillance works.

Kalshi’s head of enforcement, Robert DeNault, told The Hill that “Kalshi prohibits insider trading and market manipulation”. A person familiar with the company said it already blocks candidates and campaign staff from election markets using FEC payroll data and has set up an independent market integrity committee. Polymarket did not immediately respond to The Hill.

How big the markets are this week

The timing matters because of scale. A Coinpaper report published October 29 put Kalshi’s October volume at about $65 billion, roughly 10% above September, and Polymarket US at about $10 billion. Most of that is sports, not politics, and the figures are a reported snapshot rather than audited numbers. The table below sets the reported figures next to the two largest midterm control markets on Polymarket’s international exchange, read from its public API on October 30.

Measure	Figure	Source
Kalshi October volume (all categories)	~$65 billion	Coinpaper, Oct 29
Polymarket US October volume	~$10 billion	Coinpaper, Oct 29
Kalshi open interest	$2.05 billion	Coinpaper, Oct 29
Polymarket US open interest	$384 million	Coinpaper, Oct 29
“Which party will win the House in 2026?” volume	~$31.2 million	Polymarket API, Oct 30
“Which party will win the Senate in 2026?” volume	~$11.9 million	Polymarket API, Oct 30

The control-of-Congress markets are where insider information is least likely to matter, because no single insider knows the national result. The senators’ examples are about something narrower: individual House and Senate races, primaries and contracts on what a candidate will say or do, where a campaign staffer can know more than the market. Live prices for the national markets are on our 2026 midterm election odds page; the House contract is listed here on Polymarket.

Why a Utah Republican signed it

Warren has pushed the CFTC to restrict election and sports contracts since 2024, so her name on the letter is not new. Curtis’s is. Utah has become the most aggressive state against prediction markets: its attorney general sued Kalshi and the market maker Susquehanna in state court on October 20, the CFTC sued Utah on October 26 to stop that enforcement, and on October 28, the same day the letter is dated, Utah filed 14 criminal counts against Kalshi and its two founders. Our analysis of the Utah charges covers that case.

A bipartisan letter does two things a single-party one does not. It makes it harder to dismiss the request as a partisan attack on a sector that has close ties to the current administration, and it signals that questions about election contracts could survive a change in Senate control. Bloomberg Law noted that Warren would be likely to pursue the issue if she became chair of the Banking Committee.

What changes for traders before November 3

Nothing, directly. The letter does not suspend any market, does not alter CFTC rules and does not create a new obligation for users. Kalshi and Polymarket US remain CFTC-registered venues, and their existing rulebooks already prohibit trading on material nonpublic information. What may change is enforcement behaviour: exchanges under public scrutiny tend to tighten screening, freeze accounts faster and publicise cases, and both platforms have an incentive to show the senators concrete referrals.

Three things are worth watching. Whether either company publishes its reply, or the senators publish it for them; whether the CFTC, which has not commented on the letter, announces any referral or case tied to the midterms; and whether Congress returns to the bills that would bar election contracts outright once the results are in.

Method and limits

This article is based on the Senate Banking Committee minority press release of October 29, 2026, and reporting by The Hill, Bloomberg Law and Punchbowl News. We did not see the companies’ replies, which were not public at the time of writing. Volume and open interest figures are as reported by Coinpaper and are not audited; Kalshi’s total includes sports and other categories. Polymarket market volumes come from the public Gamma API on October 30, 2026 and refer to the international exchange, not Polymarket US. Nothing here is a prediction of how any race will resolve.

Frequently asked questions

What did Warren and Curtis ask Kalshi and Polymarket?

In a letter dated October 28, 2026 they asked each company to describe its safeguards against insider trading, manipulation and trading on material nonpublic information in election contracts, what it does beyond screening FEC filings, and which election insider trading cases it has referred to the CFTC.

When are the answers due?

The senators asked for responses by Election Day, Tuesday, November 3, 2026, according to the Senate Banking Committee release.

Does the letter stop election betting on Kalshi or Polymarket?

No. A letter from two senators has no legal force. Election contracts on Kalshi and Polymarket US remain available under CFTC oversight unless a regulator or court acts.

Is insider trading on prediction markets illegal?

Trading on misappropriated material nonpublic information in CFTC-regulated contracts can violate the Commodity Exchange Act, and both exchanges prohibit it in their rules. This is general information, not legal advice.