When a president could be indicted poses an awkward question, Mr. Comey said.

He said Mr. Mueller, in writing his report, seemed to be balancing Justice Department policy with building a factual record that could be used in other circumstances, such as Congress’s power to impeach a president.

“I can tell you from personal experience … that can be misinterpreted,” he said, a glancing allusion to his own decisions in the Hillary Clinton emails case.

Contrary to his saying Thursday that corrupt intent could be inferred about Mr. Trump for his actions though, he declined to bring charges against Mrs. Clinton because, he said, such intent could not be proven.