AMSTERDAM — First, Rutger Bregman came for the globalists.

In late January at Davos, the Swiss resort where the world’s political and financial elites gather each winter, Mr. Bregman bluntly asked why his hosts do not pay more tax.

“It feels like I’m at a firefighters’ conference and no one is allowed to speak about water,” he said. “We’ve got to be talking about taxes,” he added. “Taxes, taxes, taxes.”

Three weeks later, the young Dutch historian came for the nationalists.

Invited on Fox News by Tucker Carlson, who described his earlier outburst as “one of the great moments in Davos history,” Mr. Bregman quickly questioned his host’s sincerity and accused him of being a mouthpiece for the billionaire class.

“You’re all like: ‘Oh, I’m against the globalist elite, blah, blah, blah,’” Mr. Bregman, 30, told Mr. Carlson, who responded with a foul-mouthed rant. “It’s not very convincing.”