Lou Dobbs, another Fox host, tweeted a video of himself and a guest
discussing Dr. Yan’s “great case.” Mr. Trump retweeted it.

Dr. Yan was welcomed by an audience already primed to hear her
claims. A March poll found that nearly 30 percent of Americans
believed the virus was most likely made in a lab.

“Once Tucker Carlson picks it up, it’s not fringe anymore,” said
Yotam Ophir, a professor at the University at Buffalo who studies
disinformation. “It’s now mainstream.”