President Trump walks across the South Lawn as he returns to Washington from traveling to Atlanta to speak at the National Rifle Association Leadership Forum on April 28. (Jabin Botsford/The Washington Post)

President Trump was not subtle in his letter informing FBI Director James B. Comey that Comey was being fired.

“While I greatly appreciate you informing me, on three separate occasions, that I am not under investigation, I nevertheless concur with the judgment of the Department of Justice that you are not able to effectively lead the Bureau,” it read.

In an interview with NBC’s Lester Holt published Thursday, we learned more about those three occasions. Once, Trump says, Comey told him he wasn’t under investigation while the two were dining together; the other occasions were phone calls. “I said, ‘If it’s possible, would you let me know am I under investigation?’ ” Trump told Holt. “He said ‘You are not under investigation.’ ”

It’s completely fair to doubt the accuracy of the conversation as presented, given the way in which the story about Comey’s termination has ebbed and fluctuated since Tuesday afternoon. But there’s a broader question worth considering. If the focus of an investigation asks an FBI agent whether he or she is under investigation, does the agent have to tell the truth?

“I was a criminal investigator for years, and if someone had asked me if they were under investigation and they were under investigation, I would have said no,” said Dana Ridenour, who spent 21 years with the FBI as a special agent. The reason was simple: She wouldn’t want to tip off the target of the investigation. “As a criminal investigator,” she said, “I don’t know of any reason I would have to disclose to somebody that they were under investigation.”

The investigation worrying Trump, though, isn’t a criminal investigation at this point. As Comey himself told Congress, the investigation is a counterintelligence operation. But that doesn’t seem to matter to Joseph Lewis, who was deputy assistant director for the organized crime branch before he retired in 2004.

“It depends on the situation in which it comes up,” he said. But: “No, they typically are not obligated to say” if someone is under investigation.

Steven Hooper, who retired in 2013 as an assistant special agent in charge, was more measured.

“I don’t think there’s an easy answer,” he said. “There are so many different types of investigations. There is no one answer to that question.”

Retired section chief James Pledger agreed.

“I would say it’s situational,” Pledger said. He’s been retired since 1994, but he speculated that it’s probably the case that the FBI is now expected to give an honest answer to the question. “But there are obviously sometimes cases when it’s sensitive and the agent would have to defer.”

Presented with the Trump-Comey scenario, Pledger said that Comey would probably be expected to answer honestly. That said, the honest answer was almost certainly that Trump himself was not under investigation; rather, that his campaign was. “I would suspect that, if in fact President Trump asked Mr. Comey about that, the proper answer would be no: No, personally you’re not,” he said.

Pledger offered a specific example to that point.

“I worked the Watergate case back in the early ’70s,” he said. “I listened to the president’s tapes. There was a period of time when President Nixon wasn’t under. … It was all his staff. It wasn’t until they found some tapes and some other things. You could argue whether it was an ethical issue or a criminal investigation.” In other words, Trump probably isn’t under criminal investigation personally at the moment — but there’s certainly precedent for that situation changing as facts emerge.

For what it’s worth, Lewis, the former deputy assistant director, was skeptical that the conversation with Comey occurred as Trump presented it.

“I cannot even conceive that that kind of a conversation would go on,” he said. “I’ve worked with Comey, and I have high regard for him. I cannot believe that that’s something that he would say. That just doesn’t ring true.”

Which, again, is another question entirely.