Mr. Hatcher repeatedly predicted that the city was about to turn the corner. “I think we’re on the verge of a great new surge forward,” he said in a 1978 interview in The New York Times, and he sounded similar refrains in his re-election campaigns.

He and his supporters argued that racism was a major force in Gary’s continuing slide.

Citing a “tremendous” departure of existing businesses and private investment money in the 1978 interview, he charged, “There’s almost a vested interest among a lot of powerful business people, the tax assessors and other county officials who keep business taxes low here, in proving that a city run by a black will fail.” He also maintained that the federal government had provided too little aid.

Urban affairs experts have pointed to the volatile economic history of the steel industry and its automation of recent decades. The United States Steel Corporation founded the city in 1906 to house workers in the huge mill it was building in the area, and the mill was long Gary’s largest employer. Its cycle of layoffs and recoveries impeded lasting economic stability in the city, and the automation later reduced jobs permanently.

When Mr. Hatcher left office, there were fewer than 10,000 people working at the mill, less than half the number when he was elected 20 years earlier. (Gary’s decline continued after his mayoral tenure: The 2010 census recorded a 37 percent poverty rate in a population of 80,000.)

The mayor’s critics accused him of contributing to the city’s Rust Belt descent by squandering the federal money and, as one put it, by “chasing a national image and neglecting Gary.”

Mr. Hatcher’s explanations and promises of better times prevailed in his first four re-election campaigns, in which all his major opponents were also black. But the criticisms won out in the fifth when another black Democrat, Thomas V. Barnes, soundly beat him in the 1987 Democratic primary — and again when Mr. Hatcher tried to oust Mr. Barnes four years later.