"I say it’s enough," Trump said as he left the White House Wednesday.
The president’s comments, together with the White House’s plans to spurn Democrats’ demands for interviews, documents and information in a range of inquiries, could escalate tensions between Democrats and the Trump administration, and lead to a major legal battle over the balance of power between the executive and legislative branches.
As Democrats prepare to follow up on the special counsel's findings with a new round of witness hearings and interviews, White House lawyers are expected to tell attorneys for current and former administration witnesses that they will likely assert executive privilege over testimony, according to a source familiar with the matter.
On Monday, House Judiciary Committee Chairman Jerry Nadler issued a subpoena for the committee to publicly question McGahn about his discussions with the special counsel. McGahn cooperated with Mueller’s investigation and extensively detailed his interactions with the president in contemporaneous notes. The White House asserted no privilege over McGahn’s testimony to special counsel investigators.
The report describes Trump’s efforts to get McGahn to remove the special counsel and deny news reports about his actions after the fact.
Bill Burck, McGahn’s attorney, has been in touch with both the White House and Judiciary Committee about the request, according to a source familiar with the conversations. The White House is expected to fight Nadler’s subpoena for McGahn and could also challenge the committee's efforts to obtain additional voluntary testimony from Mueller and other witnesses from the Justice Department and administration.
Attorney General Bill Barr told reporters last Thursday he had no problem with Mueller testifying before Congress.
"Our request covers the subjects described by Mr. McGahn to the Special Counsel, and described by Special Counsel Mueller to the American public in his report. As such, the moment for the White House to assert some privilege to prevent this testimony from being heard has long since passed," Nadler said in a statement.
White House officials reiterated that the president has not made a final decision to invoke executive privilege, but insisted it remained a possibility.
"Executive privilege is on the table -- it's his right. We should note there's been a great deal of executive collaboration and compliance," White House counselor Kellyanne Conway told reporters Wednesday. "What else is there to know, what else is there to see?"
The president's ability to claim executive privilege is also hanging over separate inquiries.
On Wednesday, a lawyer for Justice Department official John Gore said Barr directed his client not to appear before the House Oversight Committee this week without the presence of agency counsel, defying Democrats’ subpoena for his testimony about efforts to add a citizenship question to the 2020 census.
The White House has also directed a former White House official not to cooperate with a subpoena from the House Oversight Committee in its investigation of the security clearance process. Chairman Elijah Cummings said he would prepare to hold Carl Kline, the former White House and current Pentagon official, in contempt of Congress.
"These employees and their personal attorneys should think very carefully about their own legal interests rather than being swept up in the obstruction schemes of the Trump Administration," Cummings said in a statement Wednesday.
It’s unclear what sort of contempt citation Democrats would advance, or whether the Justice Department would take up a criminal citation passed by the House. Democrats could also pursue contempt through civil litigation.
Separately, Treasury Secretary Steve Mnuchin informed the House Ways and Means Committee that it would miss the panel’s deadline to turn over six years’ of the president’s tax returns, and is continuing to review the request with the Justice Department and plans to respond by May 6. Democrats, who requested the information under a 1920s provision of the tax code, could go to court to compel the administration to comply with the law.
The president’s personal legal team has also sued the House Oversight Committee in an effort to prevent a financial accounting firm from turning over ten years’ of his records under a subpoena, arguing that Democrats’ request served no legislative purpose. Democrats have said they need to investigate whether the president, the first modern president not to release his tax returns, has any conflicts of interest that are impacting his official duties.
In an interview with the Washington Post on Tuesday, Trump said Democrats were attempting to damage him politically in their oversight investigations.
"There is no reason to go any further, and especially in Congress where it’s very partisan — obviously very partisan," Trump told the newspaper.
Trump did not sit for an interview with Mueller. He submitted written answers to questions about whether his campaign coordinated with Russia, but not regarding any potential obstruction of justice. The special counsel’s office wrote in an appendix to its report that it found some of Trump’s answers to be "inadequate ... in several respects."
The Trump administration isn’t the first to challenge the legitimacy of some congressional investigations, Douglas Kriner, a political scientist at Cornell University, told ABC News. But the president and White House’s effort to defy a range of inquiries could prompt a larger legal reckoning on the balance of power between the two branches of government.
"The consequences are huge," he said. "The pendulum of power could swing even further from one end of Pennsylvania Avenue to another."
Legal experts also raised questions about Trump's ability to claim executive privilege.
"Given that the president waived executive privilege previously, it is difficult to switch and claim it later," said Mark Rozell, Dean of the Schar School of Policy and Government at George Mason University. "Nonetheless there may be differences regarding congressional testimony as opposed to cooperating with a special counsel investigation that would lend merit to a claim of executive privilege. The president may have had some confidence that a special counsel producing a redacted report would preserve some secrecy while fearing disclosure by a legislative committee," Rozell said.
"As a private citizen no longer employed by the White House, McGahn can determine for himself whether he will comply with the subpoena. I don't see how the administration has authority to prohibit a private citizen from appearing before Congress," said Nancy Kassop, a political science professor at State University of New York at New Paltz.
"If the administration persists in its position, and if McGahn does not comply with the subpoena, then, Congress may cite him for contempt. However, enforcing a contempt citation would require the Justice Department to bring a criminal prosecution against McGahn, and given the recent actions of Attorney General Barr, it is unimaginable that he would proceed down that road, Kassop said. "Still, one suspects that McGahn would not be eager to be cited for contempt of Congress, even if there is no likelihood of enforcement.
"As for any assertion of privilege on the part of McGahn, three federal courts of appeals (DC Circuit, 7th Circuit and 8th Circuit) have all ruled that a government lawyer cannot claim government attorney client privilege when evidence is sought by a grand jury about alleged crimes within the executive branch," she said.
Louis Fisher, a constitutional scholar with the Project on Government Oversight, said that McGahn will probably have to testify, even though the president might still be able to keep him from divulging certain information.
Fisher said that he has never heard of executive privilege being successfully used to keep someone from testifying altogether, and that it would be a new argument.
ABC News' Lauren Pearle contributed to this report.