Experts war-gamed what might happen if deepfakes disrupt the 2024 election. Things went sideways fast.

It’s Election Day in Arizona and elderly voters in Maricopa County are told by phone that local polling places are closed due to threats from militia groups.

Meanwhile, in Miami, a flurry of photos and videos on social media show poll workers dumping ballots.

The phone calls in Arizona and the videos in Florida turn out to be “deepfakes” created with artificial intelligence tools. But by the time local and federal authorities figure out what they are dealing with, the false information has gone viral across the country.

This simulated scenario was...