Chris Hunter was preparing to take a health-care fraud case to trial when he says he became concerned about the dynamics at the Justice Department, the agency where he had worked for more than a decade.

After watching President Donald Trump fire former FBI Director James Comey, belittle Attorney General Jeff Sessions, and pardon Sheriff Joe Arpaio, among other events, Mr. Hunter said he decided to leave his job as a prosecutor in Tampa in December and run for Congress.

...