88% of election contracts can be moved under $1,000

Eighty-eight percent of active congressional election markets on Polymarket International, Polymarket U.S., and Kalshi can have their prices shifted by 10 cents with a single wager under $1,000. This finding comes from the Anti-Corruption Data Collective, or ACDC, a nonprofit based in Washington, D.C., which analyzed 18,000 active markets. The data highlights a structural vulnerability in platforms that increasingly serve as information sources for voters.

The risk became visible during the Los Angeles mayoral race in June, which drew more than $47 million in trades, making it the most heavily traded mayoral contest of 2026. Spencer Pratt, a former reality television star who had never held office, saw his odds on Kalshi jump from 29 cents to 45 cents on May 20 after a trader bought $1.25 million in "Yes" contracts. Although the price reverted to previous levels within nine seconds according to Kalshi, ACDC found that the price remained three cents higher for two hours. This sustained deviation can alter how observers interpret market sentiment.

Pratt finished third in the primary, contradicting the 78% chance of advancing to the runoff that one market assigned him on the eve of the election. Dean Logan, the registrar-recorder for the Los Angeles County Clerk's Office, stated that prediction markets add to confusion when people treat their projections as more authoritative than actual votes. The discrepancy between speculation and results raised concerns that markets could be manipulated to inflate a candidate's perceived support.

ACDC identified 38 of 167 congressional markets worth more than $100,000 that experienced price spikes of 30 cents or more. In one instance involving Illinois Senate candidate Juliana Stratton, two large purchases totaling $8,000 drove the price of her winning contract from 47 cents to 99 cents. The price eventually settled at 52 cents, five cents higher than before the trades. Stratton won the Democratic primary two weeks later. Her office cited a poll released the same day as the spike that showed her leading, suggesting the market move aligned with existing support.

Voters are influenced by these odds. A September study funded by the Brennan Center for Justice surveyed 1,994 registered voters and found that respondents were 10 to 20 percentage points more likely to believe a candidate would win if prediction markets favored that candidate, regardless of poll results. Michelle Kendler-Kretsch, a researcher at ACDC, noted that the typical profit motive is imperfect because buying at 99 cents yields only 1 cent in profit, which transaction fees can erase. This suggests traders may have goals other than financial gain, such as influencing election outcomes.

Kalshi and Polymarket are taking steps to address these concerns. Kalshi added transparency features in October, including labels for markets with low trading activity and live feeds of individual trades. The company uses algorithms to detect unusual trading patterns but did not specify if its internal protocols triggered alerts during the Pratt trades. Polymarket rolled out an election-specific surveillance system to detect manipulation. Both platforms are governed by the Commodity Futures Trading Commission, which has rules to prevent market manipulation. However, the public cannot identify the traders behind specific bets without a subpoena or search warrant.

Shana Bautista, head of global intelligence and investigations at Polymarket, explained that the platform works with blockchain analytics firm Chainalysis to track suspicious activity. Chainalysis collects data on trade volume, total value, and profit and loss for each trader. In April, Polymarket International partnered with Chainalysis to help identify unusual patterns. The collaboration has already aided in identifying specific cases, such as a U.S. soldier charged with using classified information to bet on political events in Venezuela.