The White House on Monday blocked former counsel Donald McGahn from testifying to Congress, the latest act of defiance in the ongoing war between House Democrats and President Trump.

McGahn, who Democrats hoped would become a star witness in their investigation into whether Trump obstructed justice, was subpoenaed to testify Tuesday morning. The former White House counsel delivered critical testimony in several instances of potential obstruction by Trump detailed in special counsel Robert. S. Mueller III’s report.

“The Department of Justice 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,” said White House press secretary Sarah Sanders in a statement. “This action has been taken in order to ensure that future presidents can effectively execute the responsibilities of the office of the presidency.”

President Trump on May 13 demurred when asked if former White House counsel Donald McGahn should be held in contempt of Congress. (The Washington Post)

Trump, speaking to reporters Monday evening, called the directive “a very important precedent,” adding: “And the attorneys say that they’re not doing that for me. They’re doing it for the office of the president. So we’re talking about the future.”

The 15-page legal opinion written by Assistant Attorney General Steven A. Engel argues that McGahn cannot be compelled to testify before the committee, based on past Justice Department legal opinions regarding the president’s close advisers.

The memo says McGahn’s immunity from congressional testimony is separate and broader than a claim of executive privilege.

The immunity “extends beyond answers to particular questions, precluding Congress from compelling even the appearance of a senior presidential adviser — as a function of the independence and autonomy of the president himself,” Engel wrote.

That immunity, the memo insists, does not evaporate once the adviser in question leaves the government, because the topics of interest to Congress are discussions that occurred when the person worked for the president.

As a private citizen no longer in the government, McGahn is not necessarily bound by the White House directive, or the Office of Legal Counsel memo, to refuse to comply with the subpoena. In a letter to the committee obtained by The Washington Post, McGahn’s lawyer, William A. Burck, said the former counsel would not testify.

“Mr. McGahn remains obligated to maintain the status quo and will respect the President’s instruction,” Burck wrote.

Testifying could jeopardize business and professional standing for McGahn, who works for Jones Day, a Republican law firm with close ties to the Trump campaign and electoral politics. Jones Day will still be involved in the reelection effort, campaign officials say, but will have a reduced role from 2016, when it was the main firm.

The move to bar McGahn from answering lawmakers’ questions angered House Democrats already eager to hit back at what they view as White House stonewalling. The defiance raises the possibility that the House will hold McGahn in contempt of Congress, as House Judiciary Committee Chairman Jerrold Nadler (D-N.Y.) has threatened.

“It is absurd for President Trump to claim privilege as to this witness’s testimony when that testimony was already described publicly in the Mueller report,” Nadler said in a statement. “Even more ridiculous is the extension of the privilege to cover events before and after Mr. McGahn’s service in the White House.”

The chairman said the committee would still meet on Tuesday morning, and “Mr. McGahn is expected to appear as legally required.”

An increasing number of frustrated Democrats also want to begin impeachment proceedings against Trump even though House Speaker Nancy Pelosi (D-Calif.) last week privately downplayed the possibility and encouraged her members to focus on their policy agenda.

Some Democrats believe that opening an impeachment inquiry would strengthen their hand in trying to force the White House to comply with document requests and witness testimony, including McGahn’s.

House Democrats were hoping to make McGahn their key witness as they seek to unpack the findings of the Mueller report — particularly regarding questions of whether Trump obstructed justice. Trump and his administration have thwarted multiple House probes into the report, the president’s businesses and efforts to obtain his tax returns, frustrating Democrats who said they are trying to conduct oversight.

McGahn emerged as a central player in Mueller’s findings, a senior confidant who documented in real time Trump’s rage against the Russia investigation and efforts to shut it down. Democrats wanted him to testify for a national television audience about the two episodes in which Mueller found McGahn was a critical witness and in which investigators say they have substantial evidence that Trump was engaged in obstruction of justice that would normally warrant criminal charges.

In mid-June of 2017, Trump tried to pressure McGahn to intervene with the Justice Department to try to push for Mueller’s removal from office based on alleged conflicts of interest, the report said. Then, in February 2018, Trump summoned McGahn to the Oval Office and urged him to deny a news account that suggested the president asked for his help in ousting Mueller.

The McGahn confrontation carries echoes of another former White House lawyer who was subpoenaed by Congress — Harriet Miers, a former adviser to President George W. Bush. Congress held her in contempt in 2007 for refusing to comply with a subpoena in its investigation of the firings of U.S. attorneys. As with McGahn, the administration took the position that Miers’s departure from the government did not leave her susceptible to a congressional subpoena.

The Justice Department memo released Monday said the “immunity of the president’s immediate advisers from compelled congressional testimony on matters related to their official responsibilities has long been recognized and arises from the fundamental workings of the separation of powers. Those principles apply to the former White House Counsel. Accordingly, Mr. McGahn is not legally required to appear and testify about matters related to his official duties as Counsel to the President.”

The McGahn news was not surprising. Earlier this month, the White House invoked executive privilege to bar McGahn from complying with a congressional subpoena to provide documents to Congress related to Mueller’s investigation, although the White House never officially filed the paperwork to assert the White House secrecy prerogative.

In a letter to the House Judiciary Committee earlier this month, White House counsel Pat A. Cipollone said McGahn does not have the legal right to comply with its subpoena for 36 types of documents — most related to Mueller’s nearly two-year probe of Russian interference in the 2016 election. Rather, Cipollone argued that the committee needed to send the request to the White House — and he even hinted that the administration would assert privilege to block the information.

“The White House provided these records to Mr. McGahn in connection with its cooperation with the special counsel’s investigation and with the clear understanding that the records remain subject to the control of the White House for all purposes,” Cipollone wrote earlier this month. “The White House records remain legally protected from disclosure under long-standing constitutional principles, because they implicate significant executive branch confidentiality interests and executive privilege.”

Carol D. Leonnig contributed to this report.