By Election Day, Thomas Morrow had bet about $1,200 on prediction markets that Republicans would win their races—excited to have a way to put his money where his mouth was.

“It’s a wonderful opportunity to prove very clearly that I know what I’m talking about when I make my prognostications about politics to my friends,” Morrow, 64 years old, said Tuesday.

By Wednesday morning, Morrow was down about half—around $640—after Democrats staged a blowout victory in the midterm elections to recapture majorities in both the House and Senate. He was still holding out that Sen. Dan S. Sullivan (R., Alaska) would pull off a win, despite the candidate’s dwindling odds on the markets.

While voters were heading to their polling stations Tuesday, traders were risking sums large and small on a swirl of voter-turnout data, political braggadocio on social media, and—that most perilous of factors—vibes. The result was the first time that U.S. elections, a model for countries around the world, were casino-fied at scale.

Kalshi and Polymarket’s founders have marketed their platforms as more accurate than professional pollsters. But their credibility was on the line after high-profile whiffs here and abroad leading up to the midterms.

The two big platforms correctly predicted that a Blue Wave was coming. Betting markets tend to amplify polls, many of which had made the same forecast. As early votes trickled in and the tilt toward Democrats became clearer, traders piled into the likely-to-win bets, giving the impression that the markets were calling races before polls had closed.

The betting platforms also had some significant miscalculations–often missing the same races that the polls did. A little before 5 p.m. Tuesday, for instance, Kalshi showed Democrat Gina Hinojosa had a roughly 40% chance of winning the Texas governor’s race. By around 9 p.m., that shot up to around 90%. She went on to win.

For many traders, American democracy turned out to be another event to bet on—like a Sunday football game.

Most trades on Kalshi were under $10, with Polymarket bets even smaller—a sign that much of the trades were from recreational bettors, Kelly Ye, head of research at Talos, a financial technology and data firm, said Tuesday afternoon.

Large trades mostly favored Democrats. On Kalshi and Polymarket, about 90% of bets above $10,000 went to that party, while wagers under $100 were split mostly evenly, according to Ye’s research provided to The Wall Street Journal, which included data through Nov. 2.

“Larger traders tend to back the more likely outcome for a steadier return, while smaller traders lean toward long shots with a bigger potential payout,” Ye said.

While data through October showed that trading trailed 2024 volume, Kalshi said that total volume on its platform this cycle eclipsed $2.5 billion. Polymarket, which is much smaller in the U.S., has a data partnership with Dow Jones, the publisher of the Journal.

Bettors had their pick of more than 200 markets to wager on. The most popular were broad—who will control the Senate?—but many opportunities were available to put money down on highly specific scenarios with political parlay-style trades that mimicked a betting junkie’s wildest dreams.

The nature of the platforms—which offer a binary “yes” or no “choice”–makes them an easy way to bet on election outcomes.

At a rooftop party Tuesday night in Washington, D.C. sponsored by Kalshi, Republican strategist Alex Latcham said he laid out what he called one nightmare scenario for Republicans.

With the dome of the Capitol looming behind him, Latcham said on stage that the vote count could drag on for weeks. That could leave control of the Senate in limbo, he recalled saying in front of around 200 lobbyists, fundraisers and pollsters.

On Kalshi, audience members on their phones saw the odds of Democratic control of the upper chamber shoot up to above 90%.

Data shared by Kalshi showed that on the whole, by the morning of Election Day its markets had done better than election models from several other forecasters. Still, in a blog post published Wednesday morning, Kalshi’s head of politics Ben Freeman wrote that even bettors had underestimated the extent to which a blue wave turned into a blue tsunami.

Danny Singer, a trader in California, wagered about $500,000 on electoral races this cycle, including a bet that Democrat James Talarico would win the Texas Senate race. Some he cashed out early, he said, locking in gains. “I’ve done some exiting and also reshuffling based on how my views have evolved,” he said.

Then this week, he doubled down on other bets. Polls were overestimating how many Republicans would turn out, he thought—an overcorrection from previous elections.

Before 10 p.m. Tuesday, Singer was doing a victory lap. “Won every bet I made, still just holding and will let the contracts settle,” he said in a text. “I told you, democrat polling error!”Aaron Courtney, a trader in Colorado, said he deployed nearly all of his available cash in election markets. He mostly bet on Democrats winning, and stood to lose $40,000 if there were GOP upsets.

Courtney expects to profit about $20,000. His bets, he said in a text, “couldn’t have turned out much better.”