Long months of civil disorder belie progress some U.S. mayors are making on reforms demanded by protesters and in best practices for dealing with the protests themselves.

Portland Mayor Ted Wheeler has been getting it from all sides.

After more than 80 days of protests over racial injustice and policing, one of the city’s biggest real estate developers emailed the mayor and his City Council colleagues last month, warning about businesses leaving because of the “lawlessness you are endorsing downtown.” Many businesses in the city core are still...