“Trump is a master of casting, and Gallagher is a perfect fit,” said Mr. Rieckhoff, who now hosts the Angry Americans podcast. “He’s handsome, he’s heroic, he’s got a beautiful wife. He’s a Rambo version of the same story Trump has been telling over and over: The deep state is trying to screw you, the media is bad, and the rich people don’t understand you. But I’ll stick up for you.”

The partnership is valuable for Chief Gallagher, too, Mr. Rieckhoff said, because in raising his profile in conservative circles, he can cash in on book deals, speaking engagements and other business opportunities…

On Instagram, the chief and his wife have been outspoken, touting both the president and the various consumer products they are backing. (Their Instagram account has twice blocked a New York Times correspondent who has covered his case over the past year.)

“Brotherhood isn’t just a statement, it’s a way of life,” Chief Gallagher said in a statement explaining his apparel line, called Salty Frog Gear. Described as a “coastal lifestyle brand with an edge,” it features T-shirts that read “stay salty,” and hooded sweatshirts, with a custom front pocket designed to hold a beer bottle.