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 that extended into 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." White House spokeswoman Sarah Huckabee Sanders called the allegation "absolutely ridiculous."
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 was "Lying to reduce his jail time!"
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.
Lanny Davis, a Cohen adviser, declined to comment. On Friday, as photos surfaced of Cohen wearing a hospital ID bracelet and cradling a pillow with his right arm in a sling, Davis said Cohen had undergone minor shoulder surgery.
Though Republicans stayed mostly silent, 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 "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 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 is scheduled to testify publicly before the House Oversight and Reform Committee Feb. 7. Schiff has said he wants Cohen to testify before the intelligence panel, as well.
The top Democrat on the Senate intelligence committee, Virginia Sen. Mark Warner, said Friday that he expects Cohen to talk to that panel in February. The intelligence committee interviews would most likely be behind closed doors, if Cohen does appear.
Cohen pleaded guilty in November to lying to Congress to cover up that he was negotiating the Trump Tower project 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 admitted that he lied when he told lawmakers he had never agreed to travel to Russia in connection with the Moscow project and when he said that he'd decided by the end of January 2016 that the "proposal was not feasible for a variety of business reasons and should not be pursued further."
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."
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 encouraging 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 say a sitting president cannot face criminal charges. Barr said this week that he saw no reason to change that policy.
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.
Rhode Island Rep. David Cicilline, also a Judiciary committee member, 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.
"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.
Associated Press writers Jill Colvin and Zeke Miller in Washington and Jonathan Lemire and Jim Mustian in New York contributed to this report.