On a sweltering Saturday in the suburbs of Las Vegas, inside a cool casino miles from the Strip, about 100 people lined up to see the Nelk Boys. Most of the fans were young men, in their 20s, there to meet their favorite crew of YouTube pranksters and podcasters. Two young women, in short shorts and tight tanks, handed out Happy Dad hard seltzers, part of the Nelk Boys’ growing line of merchandise.

Hours later, the Nelk Boys were inside a packed T-Mobile Arena, in the heart of the city, as Dana White, the chief executive of the Ultimate Fighting Championship, welcomed a sellout crowd to the latest U.F.C. event. Donald Trump Jr. was sitting cageside.

About two weeks later, Mr. White introduced former President Donald J. Trump at the Republican National Convention, where Senator JD Vance of Ohio was announced as Mr. Trump’s running mate. The Nelk Boys popped up there, too. Soon, they interviewed Mr. Vance on their Full Send podcast.

These repeated collisions of testosterone-fueled orbits are a campaign strategy, not a coincidence.

At a time of an immense gender gap in politics among young people — women leaning left, men leaning right — the Trump campaign has been aggressively courting what might be called the bro vote, the frat-boy flank. It’s a slice of 18-to-29-year-olds that has long been regarded as unreliable and unreachable, but that Republicans believe may just swing the election this year.

To find them, Mr. Trump and his allies have been exploring deep into the universe — a manoverse — of social media stars with male-centric audiences: the Nelk Boys, Mr. White and U.F.C., Dave Portnoy and his Barstool Sports media network, YouTubers like Jake and Logan Paul, podcasters like Theo Von and streamers like Adin Ross.