President Trump and Arnold Schwarzenegger were embroiled in a long-distance feud on Thursday after the president used a prayer breakfast speech to taunt the action star about his reality show ratings, and Mr. Schwarzenegger fired back in a video posted on Twitter.

To be clear, this is actually happening.

The fireworks began on Thursday morning, when Mr. Trump used the typically solemn occasion of the National Prayer Breakfast in Washington to needle Mr. Schwarzenegger as “a total disaster” on “The New Celebrity Apprentice,” the latest incarnation of the NBC reality franchise that catapulted Mr. Trump to national stardom.

“They hired a big, big movie star, Arnold Schwarzenegger, to take my place, and we know how that turned out,” Mr. Trump said, as Mark Burnett, the “Apprentice” creator who has become an active champion of Christian causes, listened a few feet away.