The Trump administration has blocked former White House counsel Don McGahn from testifying before the House Judiciary Committee on Tuesday, dismissing a subpoena issued by Democrats as "wasteful and unnecessary".
Mr McGahn, who served as chief White House counsel for almost two years, was a key figure in special counsel Robert Mueller's investigation into Russian interference in the election. According to the Mueller report, he told investigators that Mr Trump directed him to remove Mr Mueller from his role during the summer of 2017.
Democrats in Congress issued a subpoena last month requesting the lawyer to testify before the House Judiciary Committee as they continue investigating possible obstruction of justice by the president.
But in a statement on Monday afternoon the White House announced that the president was blocking the request, citing executive powers.
"This action has been taken in order to ensure that future Presidents can effectively execute the responsibilities of the Office of the Presidency," press secretary Sarah Huckabee Sanders said.
Arguing that the White House has been “completely transparent with the Special Counsel’s investigation,” she said that the Special Counsel had received more than 1.4 million documents and hours and hours of interviews from White House officials, including more than 30 hours from Mr McGahn.
“The Democrats do not like the conclusion of the Mueller investigation - no collusion, no conspiracy, and no obstruction – and want a wasteful and unnecessary do-over.”
The move by the administration marks the latest standoff between the Trump administration and Congress as the fallout over the Mueller investigation continues.
Though Mr Mueller found no evidence of collusion between the Trump campaign team and Russia, he did not exonerate the president in relation to obstruction of justice charges. Mr Trump has vowed to fight subpoenas issued by the Democratic-controlled House of Representatives, but Democrats maintain that they have the right to oversee the executive branch and want to investigate Mr Trump further.
In a letter to Jerry Nadler, the chairman of the House Judiciary Committee, current White House legal counsel, Pat Cipollone wrote that the Department of Justice has found that Mr McGahn is "absolutely immune" from compelled congressional testimony, even though he has since left his role in the White House and is now a private citizen.
Citing three previous legal opinions, the letter states that "subjecting a senior presidential advisor to the congressional subpoena power would be akin to requiring the President himself to appear before Congress." Previous presidents, including Barack Obama and George W Bush, used similar grounds to claim immunity from congressional investigations.
It was not immediately clear how Mr McGahn or the committee would respond.
Mr Nadler had previously threatened to hold Mr McGahn in contempt of court if he did not comply with the subpoena.
The development came as a US federal judge ruled that another congressional committee has the power to subpoena records from Mr Trump’s accounting firm, Mazars.
In a blow to the president, US district Judge Amit Mehta in Washington said that the House Oversight and Reform Committee has the authority to examine Trump’s personal and business records going back to 2011.
She rejected the argument from Mr Trump’s legal team that Congress was not entitled to the documents.
Mr Trump is likely to appeal the decision, but it marks the first time a court has weighed-in on the contentious issue of how much oversight Congress should have over the President’s financial and other affairs.