Andrews’ South Carolina upset hands prediction markets a marquee miss

Democrat Annie Andrews defeated Republican Darline Graham for a U.S. Senate seat in South Carolina, an upset that handed Kalshi and Polymarket their first high-profile forecasting failure of the 2026 midterms. Late Tuesday afternoon, both markets implied Graham had a 70% chance of winning.

The Associated Press called the race for Andrews, a pediatrician who became South Carolina’s first woman elected to the Senate. She is also the first Democrat to win a Senate seat in the state since 1998, ending a 28-year drought in a state Donald Trump carried by nearly 18 percentage points in 2024.

The contest had not been regarded as competitive by either party until recent weeks. Graham had been appointed to the seat after her brother, Senator Lindsey Graham, died in July. Andrews’ win provided Democrats a significant pickup as they sought the four seats needed for a Senate majority.

Andrews centered her campaign on affordability, calling for an end to tax breaks for wealthy people, higher wages and more affordable child care. She said her work treating children whose families struggled to pay for medicines had drawn her into politics.

The Atlantic attributed the result to Graham’s difficulties as an electoral candidate, a historically favorable national environment for Democrats and organizing that increased turnout across the state. Jaime Harrison, who lost to Lindsey Graham by more than 10 percentage points in 2020, said the factors behind the victory had aligned and described Andrews as the stronger candidate.

As this publication reported on Nov. 1, polls and prediction markets had both pointed to Democratic gains but carried many of the same risks. Prediction-market odds move with users’ bets rather than representative polling, according to the University of Washington Center for an Informed Public, and traders may pursue either likely returns or larger payouts on unlikely outcomes.

The South Carolina result came during prediction markets’ largest test yet in political forecasting. More than $1.48 billion was wagered on the midterms on Tuesday, while other competitive Senate contests drew millions of dollars in bets. The platforms gained prominence after signaling a Trump presidential victory in 2024 when traditional opinion polls suggested otherwise, though prior misses in U.S. primaries and Brazil’s presidential election had already shown their limits.

Kalshi and Polymarket have argued that events carrying comparatively low probabilities occur frequently, and that political upsets are no exception. Fox News, The Wall Street Journal and CNN announced partnerships with the platforms to incorporate election betting into coverage before the vote.