As pundits were sharing sometimes wildly different takes on how Kamala Harris and Donald Trump performed in Tuesday’s presidential debate, traders were putting money on which candidate would win the election. Those bets also told a story about the debate: On both PredictIt and Polymarket, two so-called prediction markets, the odds were swinging toward Harris.

Screenshots of the markets were seemingly everywhere — across social media, embedded in news articles, and cited by television anchors.

You’ll be hearing more about them. Platforms that facilitate wagers on politics have largely operated offshore because they were prohibited in the United States. But on Thursday, a company called Kalshi was briefly allowed to take bets from Americans on November’s elections.

Within hours of a U.S. District Court giving Kalshi the green light to offer election contracts — which regulators had tried to block — the company had posted what its C.E.O. called “the first trade made on regulated election markets in nearly a century.”

Shortly after that, the popular trading platform Interactive Brokers announced that it planned to allow similar wagers.

A federal appeals court has since temporarily blocked the bets. But the U.S. District Court decision has essentially opened the door for legal gambling on politics.