If the former F.B.I. director James Comey’s testimony to the Senate Intelligence Committee is to be believed, one of the driving factors that led Donald Trump to fire Comey was the F.B.I. chief’s reluctance to publicly state that the President was not a subject of the Russia investigation. But is he now? While the Justice Department and Robert Mueller, the special counsel, have not commented on whether they are investigating Trump, several former federal prosecutors told me that if he’s not yet, he soon will be—or at least should be.

Trump was seized with this issue. In their first meeting, at Trump Tower, on January 6th, when Comey briefed Trump on an unverified dossier claiming that Russian intelligence had recorded Trump cavorting with prostitutes in Moscow, Comey assured the President-elect that the F.B.I. “did not have an open counter-intelligence case on him,” according to Comey’s written testimony. At their dinner at the White House, three weeks later, during which Trump allegedly asked Comey to pledge his loyalty to him, the President returned to the stories about Russian hookers, which he denied, and raised the idea that perhaps Comey could investigate the matter and clear him of any wrongdoing. Comey told Trump that it was a bad idea. “I replied that he should give that careful thought because it might create a narrative that we were investigating him personally, which we weren’t,” Comey said in his testimony.

Seven weeks later, on March 20th, Comey testified before the House Intelligence Committee, and refused to confirm or deny publicly whether Trump was personally being investigated. Trump clearly became irritated by Comey’s coyness. On March 30th, Trump called Comey to tell him, according to Comey, that the Russia investigation was “ ‘a cloud’ that was impairing his ability to act on behalf of the country.” Comey tried to mollify Trump by reminding him again that he was not under investigation and explaining that he had privately informed congressional leaders of that fact. Trump fixated on that comment. “We need to get that fact out,” he said, according to Comey, who further reported that Trump, twice more in their conversation, returned to the issue of getting that information out. “I told him I would see what we could do,” Comey said. Two weeks later, on April 11th, with little action taken by Comey on communicating the fact that Trump wasn’t under investigation, the President called Comey to complain. It was their last conversation before Trump fired Comey, on May 9th.

In his letter announcing Comey’s dismissal, Trump made a point of advertising these conversations with Comey, noting, “I greatly appreciate you informing me, on three separate occasions, that I am not under investigation.” When Comey went public, last week, with his account of his interactions with Trump, the President’s defenders pounced on the fact that Comey corroborated Trump’s claim. “The President feels completely and totally vindicated,” Marc Kasowitz, Trump’s personal lawyer, said. “He is eager to continue to move forward with his agenda."

The irony in all of this is that Trump’s actions may very likely have caused him to personally come under investigation.

Former prosecutors who have served in both Republican and Democratic Administrations told me that an obstruction-of-justice case against Trump is a no-brainer. “Comey's testimony in a grand jury would be enough to get an indictment,” Julie O’Sullivan, who was part of the team that investigated Whitewater, the Clinton land deal that attracted a special prosecutor in the early nineties, said. To O’Sullivan, Comey’s detailed account of the Oval Office meeting in which Trump cleared the room and then told Comey to let go of the investigation of Michael Flynn, whom Trump had fired, the previous day, was especially damning because it showed that Trump knew that what he was doing was wrong.

“For a prosecutor, this attempt to hide the conversation, all antenna are going up,” O’Sullivan told me. “That tells you that he has a consciousness that what he’s about to do is wrong. It’s like having a bonfire with documents in the back yard. It's wonderful. Seriously, this is the best thing ever for a prosecutor.”

To be sure, there is some disagreement among former prosecutors. “I think it is very reckless for any former prosecutor to say an obstruction-of-justice case can or can’t be made based on one witness’s testimony,” Matthew Whitaker, a former U.S. Attorney who was appointed by President George W. Bush, and who ran as a Republican Senate candidate in Iowa, in 2014, said. “That makes me queasy. I’m shocked that so many former prosecutors are convicting the President of that crime.” But, among former prosecutors, Whitaker appears to be in the minority.

There is some public evidence that Mueller is taking the obstruction accusation seriously. He asked for and received all the memos that Comey wrote memorializing Comey’s interactions with Trump. Why would Mueller need those unless he was looking into possible obstruction?

When will we actually know if Trump is, indeed, under investigation by Mueller? Two events could trigger a public announcement. Rod Rosenstein, the Deputy Attorney General, talked to Trump shortly before Trump fired Comey. Rosenstein later appointed Mueller as the independent counsel, and Mueller reports to him. But, given Rosenstein’s role in Comey’s dismissal, he may end up being a witness in any obstruction investigation and would therefore have to recuse himself from that part of the inquiry, a fact that would likely be made public. At a Senate hearing on Tuesday, when Rosenstein was asked if was possible that he was a witness in Mueller’s probe, he responded, “I’m not going to be talking about the investigation.” When asked if being a witness would represent a conflict of interest, he replied, “I’m not going to answer hypothetical questions,” but he said that he and “career professionals” would “defend the integrity of that investigation.”

A second sign that Trump himself is under investigation would be if Mueller begins to interview witnesses who can corroborate Comey’s testimony and then the interviews, or subpoenas associated with them, become public. The day after Comey testified, Senator Dianne Feinstein sent a letter to Chuck Grassley, the chairman of the Senate Judiciary Committee, asking the committee to investigate whether Trump obstructed justice. She listed five witnesses who could help confirm Comey’s account of the Oval Office meeting (Andrew McCabe, the deputy director of the F.B.I.; Jim Rybicki, Comey’s chief of staff; James Baker, Comey’s general counsel; David Bowditch, the associate deputy director of the F.B.I.; and Carl Ghattas, an official in the National Security Branch of the F.B.I.). These are all allies of Comey, but Trump’s closest allies may also be important witnesses, including his son Donald Trump, Jr., who, in an interview on Fox News on Sunday, seemed to confirm Comey’s version of events. (There is no parent-child privilege in federal law, so Trump’s sons, as well as his daughter Ivanka, could be called to testify in front of a grand jury about their conversations with their father.)

It’s probably not a matter of if Trump will be personally investigated; it’s a matter of when. “There is no doubt in my mind that Mueller will investigate that,” a former federal prosecutor who served in the Obama Administration said. “Trump claims total vindication, and the thing that he was claiming vindication about was that he was not the target of a criminal investigation. But now he is—or imminently will be.”