Democrats are vowing to investigate whether President Donald Trump directed his personal attorney Michael Cohen to lie to Congress about a Moscow real estate project, calling that possibility a “concern of the greatest magnitude.” Trump’s current lawyer said the allegations sparking the inquiry are “categorically false.”

Any evidence that Trump directed a witness to lie to investigators would place him in the greatest political and legal jeopardy yet and confront him with allegations of the sort that led to the departure of one president and the impeachment of another.

At issue is a report by BuzzFeed News that Trump told Cohen to lie about negotiations over the Moscow project during the 2016 campaign. The Associated Press has not independently confirmed the report.

Trump lawyer Rudy Giuliani said in a statement Friday that “any suggestion — from any source — that the President counseled Michael Cohen to lie is categorically false.”

The report comes as House Democrats have promised a thorough look into Trump’s ties to Russia, and as special counsel Robert Mueller is investigating Russia’s meddling in the 2016 election and contacts with the Trump campaign.

Though his supporters have said Trump cannot be investigated for actions the Constitution permits him to take, even the president’s nominee for attorney general, William Barr, said at his confirmation hearing this week that a president or anyone else who instructs a witness to lie or change his testimony commits illegal obstruction of justice.

BuzzFeed, citing two unidentified law enforcement officials, said Trump directed Cohen to lie to Congress and that Cohen regularly briefed Trump and his family on the Trump Tower project in Moscow — even as Trump said he had no business dealings with Russia. BuzzFeed said Cohen told Mueller that Trump personally instructed him to lie about the timing of the project in order to obscure Trump’s involvement.

BuzzFeed said Mueller’s investigators learned about Trump’s directive “through interviews with multiple witnesses from the Trump Organization and internal company emails, text messages, and a cache of other documents.” The report says Cohen then acknowledged Trump’s instructions when he was interviewed by the Mueller team.

On Twitter, Trump charged that Cohen is “Lying to reduce his jail time!” even though Cohen has already been sentenced.

Giuliani noted that Cohen had pleaded guilty to lying and quoted federal prosecutors in New York who chastised him for a “pattern of lies and dishonesty over an extended period of time.” Mueller’s team, however, has called him a credible witness.

“Today’s claims are just more made-up lies born of Michael Cohen’s malice and desperation,” Giuliani said.

Two Democratic committee chairmen in the House said they will open inquiries.

The House Intelligence Committee chairman, Adam Schiff, D-Calif., said “we will do what’s necessary to find out” if the report was true. He said the allegation that Trump directed Cohen to lie in his 2017 testimony to Congress “in an effort to curtail the investigation and cover up his business dealings with Russia is among the most serious to date.”

Calling the allegations a “counterintelligence concern of the greatest magnitude,” Schiff said his committee had already been working to secure witness testimony and documents related to the Moscow Trump Tower deal.

The chairman of the House Judiciary Committee, Rep. Jerrold Nadler of New York, said directing a subordinate to lie to Congress would be a federal crime. He said his committee’s job “is to get to the bottom of it, and we will do that work.”

Cohen pleaded guilty in November to lying to Congress to cover up that he was negotiating the Trump Tower project in Moscow on Trump’s behalf during the heat of his presidential campaign. The charge was brought by Mueller and was the result of Cohen’s cooperation with that probe.

He was sentenced to three years in prison for crimes that included arranging the payment of hush money to conceal his boss’ alleged sexual affairs, telling a judge that he agreed time and again to cover up Trump’s “dirty deeds” out of “blind loyalty.”

White House spokesman Hogan Gidley told Fox News Channel that taking the BuzzFeed story seriously was “absolutely ludicrous,” but he repeatedly refused to deny the central allegation that Trump directed Cohen to lie.

An adviser to Cohen, Lanny Davis, declined to comment on the substance of the article, saying that he and Cohen wouldn’t answer questions out of respect for Mueller.

Though some limits of executive power are untested, there is historical precedent for a president to face consequences over similar allegations.

One of the articles of impeachment against Bill Clinton, for instance, accused him of coaching a witness to give false testimony. Richard Nixon faced similar allegations before ultimately leaving the White House.

Though Congress could use the allegation as a basis for impeachment proceedings, Justice Department legal opinions do not allow for criminal charges against a sitting president. Barr said this week that he saw no reason to change that policy.

Cohen is scheduled to testify before the House Oversight and Reform Committee Feb. 7, where he will probably be questioned about the report.

Though House Speaker Nancy Pelosi has discouraged any talk of impeachment in the early days of her new majority, some senior Democrats said that if the BuzzFeed report is confirmed, Trump’s actions could rise to that level.

“If the @BuzzFeed story is true, President Trump must resign or be impeached,” tweeted Texas Rep. Joaquin Castro, a member of the House intelligence panel.

California Rep. Ted Lieu, a member of the Judiciary committee, tweeted that it’s time for that panel “to start holding hearings to establish a record of whether @POTUS committed high crimes.”

Rhode Island Rep. David Cicilline, also a member of the Judiciary committee, tweeted that if Trump directed Cohen to lie, “that is obstruction of justice. Period. Full stop.”

A Senate Democrat, Chris Murphy of Connecticut, tweeted that “we need to know this ASAP” if Mueller does have multiple sources confirming that Trump directed Cohen to lie to Congress.

“Mueller shouldn’t end his inquiry, but it’s about time for him to show Congress his cards before it’s too late for us to act,” Murphy tweeted.