JUDGE INTRIGUED by immunity argument.

WASHINGTON — A federal judge on Thursday sharply questioned a Justice Department lawyer about President Donald Trump’s attempt to block a congressional subpoena to his former White House counsel, Donald McGahn, suggesting that the Trump administration’s legal arguments posed a threat to constitutional checks and balances.

In a lengthy argument, Judge Ketanji Brown Jackson grilled the department lawyer, James Burnham, about the executive branch’s theory that McGahn is absolutely immune from being compelled to testify — meaning he does not even have to show up — and that the House cannot ask courts to enforce its subpoenas against executive branch officials.

“The House can never go to court?” Jackson asked.

“As a general matter, I think that is correct,” Burnham replied, adding: “The Constitution does not allow this. It does not allow the House and the executive branch to sue each other in court.”

But a lawyer for the House, Megan Barbero, pointed to rulings by district judges during the administrations of George W. Bush and Barack Obama holding that Congress could file such lawsuits and that top presidential aides must show up in response to a subpoena. Burnham maintained that the courts wrongly decided those precedents, which are not binding.

Burnham said the White House’s claim of absolute immunity extended to top White House aides, whom he called “the alter ego of the president,” as well as former presidents and aides after they leave office. Such immunity goes beyond executive privilege the president might invoke to prevent aides from disclosing information in response to specific questions or topics.

Jackson expressed discomfort at how such immunity is applied when former senior officials from both major parties comment regularly in the media. “Yet for some reason, he doesn’t own it for people who are talking on MSNBC all the time?” she asked. Jackson, a 2013 Obama appointee, said she would rule as quickly as possible.

McGahn is a key witness to several episodes in the report by the former special counsel, Robert Mueller, about Trump’s alleged attempts to obstruct the Russia investigation.

The House Judiciary Committee sued McGahn in August after he defied its subpoena on Trump’s instructions.

The House asked the court to expedite the case so it could be appealed by whichever side loses.

House general counsel Douglas Letter argued that “the Judiciary Committee cannot fulfill its constitutional investigative, oversight and legislative responsibilities — including its consideration of whether to recommend articles of impeachment — without hearing from [McGahn].”

Letter said the government’s position is “the president always wins.”

“I don’t think there’s any way the Supreme Court would say, now when we’re engaged in an impeachment investigation — trying to determine if this person should no longer be president of the United States — that we cannot subpoena people” who may know whether impeachable offenses have been committed, he said.

The lawsuit states that McGahn witnessed “nearly all of the most egregious episodes of possible presidential obstruction,” and that his statements are mentioned in the special counsel’s report more than 160 times. “McGahn is uniquely positioned to explain those events, bring additional misconduct to light, and provide evidence regarding the president’s intent,” the complaint says.

William Burck, McGahn’s attorney, said in a statement that McGahn will abide by the president’s instructions absent a contrary decision from the court. McGahn “has an ethical obligation to protect client confidences,” Burck said. “Don does not believe he witnessed any violation of law. And the president instructed Don to cooperate fully with the special counsel but directed him not to testify to Congress unless the White House and the committee reached an accommodation.”