An old-school, wide-brimmed rope hat — some in white and navy, others in red and white — has seemingly become the ironic must-have fashion accessory of the summer.

It is the “Make America Great Again” campaign hat first worn in July by Donald J. Trump in Laredo, Tex., and since spotted on hipsters from Williamsburg, Brooklyn, to the Silver Lake district of Los Angeles and in the football locker of Tom Brady, not to mention on the heads of the hundreds of Trump loyalists at his rallies.

“I was certainly surprised to the extent it caught on,” Mr. Trump said in a phone interview last week. “It’s become the hottest fashion item there is.”

The hats, in four different designs, are $25 on the Trump campaign website and in Midtown at the store in the Trump Tower, where they promptly sold out.