A divisive figure who rose to national attention last year during the Republican National Convention, Mr. Clarke previously said he had been offered a Homeland Security post.
President Trump has signaled that taking the law into one’s own hands is permissible, within the executive branch or in local police departments, or even against a heckler at one of his rallies.
He served six terms as sheriff of Maricopa County in Arizona before earning a criminal conviction and a presidential pardon. The Times first covered him in 1994.
A new class of Dallas recruits trains to step into an uneasy moment in American policing.
A week after the president said he would bar transgender military personnel, officials in Texas, Ohio, Colorado and elsewhere are responding with invitations.