WASHINGTON, D.C. — Evidence is amassing that President Donald Trump used his position to obstruct an FBI investigation into his campaign’s ties with Russia.

Whether Congress chooses to act on that evidence is an open question.

Former FBI Director James Comey, fired by Trump last month, will told Congress today that the president asked him for his loyalty during a Jan. 27 dinner and then, in a Feb. 14 Oval Office meeting, pressured Comey to abandon the FBI’s investigation of Michael Flynn, Trump’s former national security adviser.

“I hope you can see your way clear to letting this go, to letting Flynn go. He is a good guy,” Comey recalls Trump as saying. “I hope you can let this go.”

Legal experts say that if his account is true, Comey’s statement looks a lot like evidence that Trump obstructed justice.

“That is the president pressuring the FBI director into ending an investigation,” said Elizabeth Goitein, a former Senate counsel who co-directs the Brennan Center’s Liberty and National Security Program at NYU School of Law. “That on the face of it looks like obstruction of justice.”

Peter Zeidenberg, a partner in the Arent Fox law firm in Washington, D.C., said Comey’s statement, released in advance of his scheduled testimony to the Senate Intelligence Committee, adds to evidence that Trump attempted to shut down the Russia investigation. Trump, he noted, told NBC anchor Lester Holt on May 11 that he was thinking “of this Russia thing” when deciding on Comey’s firing.

“Combined with a lot of other information we are hearing, this statement (by Comey) makes a plausible case for obstruction,” said Zeidenberg, a former federal prosecutor who assisted in the successful prosecution of I. Lewis “Scooter” Libby, Vice President Dick Cheney’s adviser. “It’s not a slam dunk, but it is plausible.”

But so what if it is? While the president takes an oath to uphold the nation’s legal statutes, the U.S. Constitution is unclear whether federal prosecutors can charge one with breaking the law. For decades the Justice Department has concluded it would be unconstitutional to haul a sitting president into a criminal courtroom.

“An impeachment proceeding is the only appropriate way to deal with a president while in office,” Assistant Attorney General Robert Dixon stated in 1973, the first year the Justice Department’s Office of Legal Counsel issued an opinion on the matter.

Some Democrats in Congress have called for Trump’s impeachment, with U.S. Rep. Al Green, a Texas Democrat, saying this week that he would formally start the process for impeachment in the House. But with Republicans controlling both chambers of Congress, it is unlikely such proceedings would advance in the near term, especially since Senate and House investigations are still in their early stages.

Indeed, Comey’s statement could cause Trump more political trouble than legal entanglements. It resurrected the president’s concerns about a salacious and disputed dossier that, among other things, reported that Trump had cavorted with hookers in Russia. Comey said that Trump brought the dossier up to him in a March 30 phone call.

“He described the Russia investigation as ‘a cloud’ that was impairing his ability to act on behalf of the country,” Comey wrote. “He said he had nothing to do with Russia, had not been involved with hookers in Russia, and had always assumed he was being recorded when in Russia. He asked what we could do to ‘lift the cloud.’ I responded that we were investigating the matter as quickly as we could, and that there would be great benefit, if we didn’t find anything, to having our done the work well.”

In his prepared statement, Comey also said that he told Trump on several occasions that the president personally was not a focus of the FBI investigation. That verifies a claim made repeatedly by Trump, who has called investigations into his campaign’s Russia ties a “witch hunt” and a “total hoax.” Trump’s outside lawyer, Marc Kasowitz, said Wednesday that the president feels “totally vindicated” by Comey’s prepared testimony.

Comey’s claims about being pressured by Trump could become a focus of the probe by Robert S. Mueller, the former FBI director appointed to serve as a special counsel overseeing the investigation into possible collusion between Russia and the Trump campaign. “We don’t know if Mueller is investigating potential obstruction of justice,” said Goitein. “But he has leeway to do so.”

Mueller would also be in a position to subpoena the nation’s top intelligence chiefs, who appeared before the Senate Intelligence Committee on Wednesday but declined to say if Trump pressured any of them to halt Comey’s Russia probe.

If Mueller were to issue a finding that Trump did seek to obstruct the FBI investigation, it would ramp up the pressure on the Senate and House to act.

“It’s a political question,” said Zeidenberg. “But one with a legal component.”