Yet so far, Mr. Trump has failed in his attempt to capitalize politically on his inflammatory remarks about the unrest in Kenosha, Wis., where last month demonstrators burned a number of buildings following the police shooting of Jacob Blake. Mr. Blake remains hospitalized after being shot seven times in the back during a confrontation captured on video and later broadcast online.

Nearly one in five Wisconsinites who said that riots in American cities were a bigger problem than racism in the criminal justice system planned to vote for Mr. Biden — even though it is Mr. Trump who is vowing a severe federal crackdown on violent outbursts.

Scott Lacko, a 55-year-old from the northern Wisconsin community of Eagle River, backed Mr. Trump in 2016 but will be voting for Mr. Biden this fall. The riots concern him deeply; he argued that Black people shot by police would have been spared had they followed instructions and said that “it’s sad to see these individuals continue to be placed on a pedestal.” But he said that Mr. Trump’s law-and-order push had not won him over.

The president, Mr. Lacko said, cannot be trusted to act in anyone’s interest but his own.