Todd Brassner, who died in a fire at Trump Tower on Saturday, loved fast cars, electric guitars, expensive watches and making long, erudite pronouncements about art and art history. He was an art dealer with health problems and a 2015 bankruptcy that listed his apartment as the location of more than $3 million worth of artwork and other collectibles, including a 1975 portrait of Mr. Brassner painted by Andy Warhol.

Friends of Mr. Brassner said he had been trying to move since the election of President Trump in 2016, which brought increased security and activity to the building on Fifth Avenue in Manhattan, but he could not sell his 50th-floor apartment, which he estimated to be worth $2.5 million in 2015.

“It haunts me,” said Stephen Dwire, 67, a musician and music producer who had been friends with Mr. Brassner since they were 14-year-olds in Harrison, N.Y., in Westchester County. “He said, ‘This is getting untenable,’” Mr. Dwire said. “It was like living in an armed camp. But when people heard it was a Trump building, he couldn’t give it away.”

Mr. Brassner, 67, lived alone amid a collection of about 100 vintage electric guitars, 40 guitar amplifiers dating to the 1930s, 150 ukuleles and artwork by Robert Indiana, Mati Klarwein, Jack Kerouac and others.