Two years ago, when the mayor’s office in St. Louis announced a $311,000 contract to tear down an old shoe factory, it made a point of identifying the demolition company as minority owned.

That was welcome news. The Missouri city was still grappling with racial tensions from the 2014 fatal police shooting of Michael Brown, a black 18-year-old, in nearby Ferguson. After angry protests, elected officials had pledged to set aside more government work for minority-owned firms.