WASHINGTON—Late Sunday, a group representing thousands of FBI agents told its members it was optimistic about the agency’s future, in part because its new director, Kash Patel, had assured the group he would choose a deputy from among their ranks.

Bongino has never served in the FBI. But his rise as a ferociously loyal right-wing influencer is what Trump wanted, says a Trump adviser.

Bongino, a former Secret Service agent, has been criticized for spreading several conspiracy theories as a talk show host.