Patsy Widakuswara at the White House contributed to this report.
The White House, acting on a legal opinion from the Justice Department, has instructed its former counsel not to testify before Congress.
Lawyer Don McGahn, facing a subpoena from the House Judiciary Committee, had been scheduled to appear before lawmakers Tuesday morning.
"They're doing that for the office of the presidency for future presidents," said President Donald Trump of the Justice Department legal opinion. "They're not doing that for me."
"I think we've been the most transparent administration in the history of our country," replied Trump to a reporter asking why not just let McGahn testify so the public can have full answers to executive action regarding the Russia investigation. "We want to get on with running the country."
Trump spoke on the White House South Lawn before boarding Marine One for Joint Base Andrews. From there, he headed to a political rally in Pennsylvania on Air Force One.
Earlier in a statement, White House press secretary Sarah Sanders explained that the Justice Department "has provided a legal opinion stating that, based on long-standing, bipartisan, and Constitutional precedent, the former Counsel to the President cannot be forced to give such testimony, and Mr. McGahn has been directed to act accordingly."
The Justice Department, in its legal opinion, states: "We provide the same answer that the Department of Justice repeatedly provided for five decades: Congress may not constitutionally compel the President's senior advisers to testify about their official duties."
In a letter to House Judiciary Committee Chairman Jerry Nadler, the current White House Counsel to the President, Pat Cipollone, states that Trump has directed McGahn not to appear at Tuesday's hearing.
"This long-standing principle is firmly rooted in the Constitution's separation of powers and protects the core functions of the Presidency, and we are adhering to this well-established precedent in order to ensure that future Presidents can effectively execute the responsibilities of the Office of the Presidency," Cipollone writes.
Democrat Nadler, in a subsequent statement, called the move by the executive branch "the latest act of obstruction" and the Trump administration's "disdain for law."
Nadler said his committee would convene on Tuesday morning "and Mr. McGahn is expected to appear as legally required."
McGahn's attorney, William Burck, however, confirmed Monday evening that his client would not appear Tuesday before the House committee.
"Mr. McGahn remains obligated to maintain the status quo and respect the President's instruction. In the event an accommodation is agreed between the Committee and the White House, Mr. McGahn will of course comply with that accommodation," Burck said in a statement.
The Democrats have been eager to hear from McGahn, including questioning him about potential obstruction of justice by Trump based on episodes outlined in the reporter of special counsel Robert Mueller.
Nadler stated last week he was prepared to have his committee vote to hold McGahn in contempt of Congress if the former White House counsel defied the subpoena.
One member of the committee is calling for an impeachment inquiry against the president to commence if McGahn does not testify Tuesday.
"We simply cannot sit by and allow this president to destroy the rule of law, to subvert the Constitution," Congressman David Cicilline of the state of Rhode Island said during an interview on MSNBC.
McGahn was also instructed by the White House, asserting executive privilege, earlier this month to hand over documents the House committee had subpoenaed.
McGahn's name is mentioned on more than 65 pages of the 448-page Mueller report.
Monday's pushback by the Justice Department and the White House is the latest instance of the executive branch trying to challenge for power the legislative branch of government with Trump betting the third branch — the judiciary — will back him up with rulings by federal judges, including the Supreme Court.
"That's a dangerous game to play, though, because the judiciary is also not going to want to see erosion of their power, even if they see congressional power getting eroded," predicted Shannon Bow O'Brien, a government professor at the University of Texas.