Prediction markets, the online platforms where people buy and sell shares tied to the outcome of future events, are booming. Combined monthly trading volume on the two biggest, Kalshi and Polymarket, hit $53 billion in July, more than double what it was in May.

Americans can bet on something as low stakes as whether President Donald Trump will say "sleepy Joe" this week or as high stakes as who will control Congress. CNN runs a live Kalshi ticker during segments that feature the data, while CNBC and Fox have signed their own deals with the company, just in time for the midterm elections.

The more mainstream these markets become, the more they invite corruption. Candidates and campaign staffers can profit from information the public doesn't have, such as an internal poll or a decision to drop out of a race. And now that the odds are on TV, anyone with enough money has a reason to try to move them.