Senators Warren and Curtis press Kalshi and Polymarket on election insider trading days before the midterms
Democrat Elizabeth Warren and Republican John Curtis wrote to the heads of Kalshi and Polymarket on 28 October asking how they stop candidates, campaign staff and other insiders from trading on election markets. What the letter asks, the cases it cites, how the companies replied, and what it means for the 3 November election markets.
In this article
- The letter at a glance
- What the senators want to know
- The cases the letter cites
- How the companies responded
- Why now
- Where the key races stood when the letter landed
- What counts as insider trading in an election market?
- How the exchanges are supposed to police this
- What it means for the 3 November markets
- What happens next
- Frequently asked questions
- Key points
- Related reading
Two senators from opposite parties want to know whether Kalshi and Polymarket can keep insiders out of their election markets. Senator Elizabeth Warren, a Massachusetts Democrat, and Senator John Curtis, a Utah Republican, sent a letter on Wednesday, 28 October 2026 to Kalshi's chief executive, Tarek Mansour, and Polymarket's chief executive, Shayne Coplan.
"We write to express concerns about election-related prediction markets and to request specific information about your companies' efforts to prevent insider trading, market manipulation, and wagers based on material nonpublic information," they wrote, as quoted by The Hill.
The letter arrives six days before the 3 November midterms, when election contracts on both exchanges are trading at record levels. Here is what it asks, what it cites and how the companies have responded.
The letter at a glance
| From | Sen. Elizabeth Warren (D-Mass.) and Sen. John Curtis (R-Utah) |
| To | Tarek Mansour (Kalshi) and Shayne Coplan (Polymarket) |
| Sent | Wednesday 28 October 2026 |
| Subject | Insider trading and manipulation in election markets |
| Context | Six days before the 3 November midterms |
Sources: The Hill and Bloomberg Law, 29 October 2026, and the Senate Banking Committee's minority press release.
Warren is the senior Democrat on the Senate Banking Committee and a long-time critic of prediction markets. Curtis is a first-term Republican from Utah, the state whose attorney general has just filed criminal charges against Kalshi. Their joint letter shows that concern about election betting now crosses party lines.
What the senators want to know
The Hill summarised the requests:
- What the companies do to stop insiders from trading, beyond checking Federal Election Commission filings. The senators name campaigns and "other individuals with access to material nonpublic information."
- Which cases of election-related insider trading each company has referred to the Commodity Futures Trading Commission.
- What safeguards are in place now ahead of the vote.
Bloomberg Law reported that the letter also voices concern about the legitimacy of these bets and "their avoidance of enforcement regimes that are designed to protect consumers."
The cases the letter cites
According to The Hill, the senators pointed to:
- Candidates trading on their own races on Kalshi, in 2025 and in April 2026. The Hill linked these cases to a CFTC press release.
- Alleged manipulation on Polymarket during the 2024 presidential election, which a Fortune report said affected "roughly one-third of the presidential market's trading volume."
"These examples raise critical questions about how many election-related transactions have escaped detection," the senators wrote. They added: "We remain skeptical that your companies can sufficiently police these [event] contracts with effective scrutiny and meaningful accountability."
How the companies responded
Kalshi pushed back. Its head of enforcement, Robert DeNault, told The Hill: "Kalshi prohibits insider trading and market manipulation and proactively blocks candidates and campaign staff from trading to protect market integrity." A person at Kalshi told The Hill that the exchange uses FEC payroll data to block candidates and staffers and has formed an independent market integrity committee.
DeNault also argued that the markets have held up against misinformation: "While fake polls have recently been promoted by major media outlets, our markets don't lie—and have been largely non-reactive to fake information or attempts to distort the odds of candidates with big trades."
Polymarket did not respond to The Hill's request for comment by publication. According to press reports, it announced election-specific surveillance on 27 October, and it is investigating suspicious trades tied to an Israeli election.
Why now
Source: Our reporting; Utah filing as reported by The Hill (13 felony counts, one misdemeanor); Polymarket price on 30 October 2026
Several things came together this week:
- Record trading. Election contracts are among the most traded markets on both platforms, and Kalshi set a volume record in October (our report).
- Utah's criminal case. Utah's attorney general filed criminal charges against Kalshi and its co-founders; The Hill reported 13 felony counts and one misdemeanor. Curtis represents Utah.
- Earlier probes. Polymarket has faced questions over suspicious bets around foreign elections, and the CFTC has opened cases on election-related trading (CFTC probe; Polymarket's midterm bets investigation).
- Money pouring in. Kalshi raised $1 billion at a $40 billion valuation the next day (our report).
Where the key races stood when the letter landed
Prices on both exchanges were close to each other on Friday afternoon, 30 October, which suggests no single trader was pushing one venue far out of line:
| Market | Polymarket | Kalshi |
|---|---|---|
| Democrats win the Senate | 72.5% | 70.5% |
| Democrats win the House | 93.5% | 92.5% |
| Texas Senate: James Talarico (D) | 71.5% | 70.5% |
| Michigan Senate: Abdul El-Sayed (D) | 77.5% | 75.5% |
| Maine Senate: Troy Jackson (D) | 68.5% | 67.5% |
| Kansas Senate: Adam Hamilton (D) | 54.5% | 52.5% |
| Iowa Senate: Ashley Hinson (R) | 55.5% | 55.5% |
Mid-points of each market's best bid and ask, 30 October 2026, about 15:50 UTC. Our price comparison study covers 351 such matched outcomes.
One pattern stands out across these races: Republicans tend to be priced a point or two higher on Kalshi than on Polymarket's international site. That is a difference between the two customer bases, not evidence of manipulation, but it is the kind of gap surveillance teams watch.
What counts as insider trading in an election market?
In stock markets, insider trading means trading on material, nonpublic information about a company. In election markets the idea is similar but harder to police:
| Who | Why it is a problem |
|---|---|
| Candidates | Can influence their own result, or know they will drop out |
| Campaign staff | See internal polls and strategy |
| Election officials | May see counts or procedural decisions early |
| Pollsters | Know results before publication |
| Anyone moving prices on purpose | Big trades can be used to create a false impression of momentum |
Both exchanges' rules ban trading on material nonpublic information and manipulation. The question in the letter is enforcement: how they find people who break the rules, and whether they report them.
How the exchanges are supposed to police this
Both Kalshi and Polymarket US are registered with the CFTC as exchanges, which means they must monitor trading and act against manipulation. In practice that involves three things:
- Blocking known insiders. Kalshi says it uses FEC payroll data to stop candidates and campaign staff from opening positions in their own races.
- Surveillance. Automated systems flag unusual trades, such as large orders just before news, clusters of new accounts, or one trader on both sides of a market (wash trading).
- Referrals. Cases are referred to the CFTC, which can bring enforcement actions. The senators want to know how many such referrals each company has made.
Polymarket's international site, which handled all of its 2024 election trading (Polymarket US only launched in December 2025), is not a US-registered exchange, which is why the senators' concerns about 2024 focus on it.
What it means for the 3 November markets
In the short term, probably nothing for prices. A letter from two senators does not change any rule, and the markets will settle on official results as usual. Our guide to when races get called explains how settlement works on election night.
In the longer term, the letter adds to the pressure on election markets in Congress at a moment when the CFTC is moving the other way, proposing to define event contracts as swaps under its own jurisdiction (our report). If the companies' answers are thin, expect hearings or legislation in the new Congress.
For traders, it is a reminder of what the exchanges already prohibit. If you work on a campaign, for an election office or for a pollster, do not trade those races. Our explainer on insider trading on Kalshi and Polymarket covers the rules and recent cases.
What happens next
No deadline for the companies' answers has been reported. A few things to watch:
- The answers themselves. The senators asked for specific numbers, including referrals to the CFTC. Whether Kalshi and Polymarket publish their replies, or the senators do, will show how much enforcement is actually happening.
- Election night. Trading volume will peak on 3 November. Any unusual trade around a race call is likely to be scrutinised.
- The new Congress. Warren is the senior Democrat on the Banking Committee, so the issue can come back as hearings or legislation when the new Congress meets in January 2027.
- The courts and the CFTC. The bigger questions about whether states can regulate these markets are moving through the federal courts and the CFTC's rule-making, not Congress.
Frequently asked questions
Who sent the letter?
Senators Elizabeth Warren (D-Mass.) and John Curtis (R-Utah), on 28 October 2026.
What do they want?
Details of how Kalshi and Polymarket stop insiders from trading election contracts, which cases they have referred to the CFTC and what safeguards are in place.
Is it illegal to bet on elections on Kalshi or Polymarket?
Trading election contracts on CFTC-regulated exchanges is legal for eligible US users; trading on inside information or manipulating prices is not. State rules vary: is Kalshi legal in your state.
Does the letter change anything before Election Day?
No rule changes. The markets will trade and settle as usual.
Key points
- Senators Elizabeth Warren (D) and John Curtis (R) wrote to Kalshi's Tarek Mansour and Polymarket's Shayne Coplan on 28 October 2026.
- They asked how the companies stop insiders from trading election contracts and which cases they have referred to the CFTC.
- The letter cites candidates trading their own races on Kalshi and alleged wash trading on Polymarket in 2024.
- Kalshi says it blocks candidates and staff using FEC payroll data; Polymarket had not commented.
- The letter adds bipartisan pressure on election markets days before the midterms.
Related reading
- Insider trading on Kalshi and Polymarket
- Midterm election predictions 2026
- Election Day 2026: what to know
- Kalshi raises $1 billion at a $40 billion valuation
- Is Kalshi legal?
This article reports the senators' letter as described by The Hill, Bloomberg Law and the Senate Banking Committee's minority staff, and the companies' public statements.
