But events like it, as well as speaking engagements featuring far-right supporters of the president, have become part of the political landscape during the Trump era. Islamophobic taunts can be heard at his rallies. Hate speech and conspiracy theories are staples of some far-right websites. If Trumpstock was modest in size, it stood out as a sign of extremist public support for a sitting president.

And these supporters have electoral muscle in key areas: Mr. Trump outperformed Mitt Romney, the 2012 Republican nominee, in rural parts of Arizona like Mohave County, where Golden Valley is located. Mr. Trump won 58,282 votes in the county, compared to 47,901 for Mr. Romney, though Mr. Romney carried the state by a much bigger vote margin.

Arizona will be a key battleground state in 2020: Democrats already flipped a Senate seat and a Tucson-based congressional district from red to blue in 2018. For Mr. Trump, big turnout from white voters in areas like Mohave County — and in rural parts of other battlegrounds like Florida, Michigan, Minnesota and Georgia — could be a lifeline in a tight election.

“We like to call this the ‘Red Wall of Arizona,’” said Laurence Schiff, a psychiatrist and Republican campaign official in Mohave County who organizes in support of Mr. Trump’s campaign. “Winning the state starts here, with us.”

Grass-roots gatherings play a critical role in the modern culture of political organizing, firing up ardent supporters and cementing new ones. Small circles of Trump-supporting conservatives, often organized online and outside the traditional Republican Party apparatus, engage in more decentralized — and explicit — versions of the chest-beating that happens at Mr. Trump’s closely watched political rallies.