The House committee investigating the Jan. 6 attack on the Capitol sent Stephen K. Bannon’s lawyer a stern letter Friday informing him that the panel rejected his arguments for failing to cooperate — and would probably proceed to vote on holding the adviser to former president Donald Trump in contempt of Congress.

Bannon has said that he should not have to comply with a subpoena from the panel because Trump is asserting executive privilege to shield his activities and those of his aides and allies from congressional scrutiny.

“The Select Committee believes that this willful refusal to comply with the Subpoena constitutes a violation of federal law,” Committee Chairman Bennie G. Thompson (D-Miss.) wrote in a previously undisclosed letter sent Friday to Bannon’s lawyer, Robert Costello.

The emphatic tone of the letter and legal arguments it lays out underscore the committee’s desire to move quickly and aggressively to combat any attempts to slow down or scuttle its investigation. The panel is scheduled to meet Tuesday evening to vote on the contempt charge against Bannon, which it is expected to approve, and it is possible the vote could be taken up by the full House as early as this week. The matter would then go to the Justice Department.

The House select committee investigating the attempted insurrection at the Capitol on Jan. 6 faces an uphill battle with former Trump administration officials. (Blair Guild/The Washington Post)

Costello did not respond to a request for comment.

On Monday, Trump sued to block the committee from receiving records for its investigation, arguing that the records requests are overly broad and have no legislative purpose. The suit also attacks President Biden for not asserting executive privilege to protect the information.

“The Committee’s request amounts to nothing less than a vexatious, illegal fishing expedition openly endorsed by Biden and designed to unconstitutionally investigate President Trump and his administration,” the suit reads. “Our laws do not permit such an impulsive, egregious action against a former President and his close advisors.”

The committee’s move to hold Bannon in criminal contempt has already sparked a debate among legal experts about whether its aggressive posture will result in the speedy results panel members said are critical to the success of their inquiry.

Contempt of Congress is a misdemeanor criminal offense that can result in up to one year in prison and a fine of up to $100,000. Criminal contempt can be pursued only by the Justice Department, setting up potential bureaucratic and legal hurdles. The committee can pursue civil contempt charges without the involvement of the Justice Department, but that has historically produced substantial delays.

In addition to Bannon, the committee has subpoenaed documents and testimony from other key Trump advisers, including former White House chief of staff Mark Meadows, former deputy chief of staff Dan Scavino and Kash Patel, a former national security and Defense Department aide.

Unlike Bannon, committee staffers have said, the others have “engaged” with the panel, and their deadlines for providing information were extended.

In declining to cooperate, Bannon’s lawyer wrote Thompson last week that his client had been contacted by Trump’s lawyer Justin Clark and instructed not to respond to the committee’s demands citing Trump’s claim of executive privilege.

Costello said that until the panel reaches an agreement with Trump or a court instructs Bannon to cooperate, his client “will not be producing documents or testifying.”

Thompson responded harshly to Bannon’s lawyer in the Friday letter as well as in another previously undisclosed letter obtained by The Washington Post sent the previous week.

First, Thompson said “the former president has not communicated any such assertion of privilege” to the committee. His stated intention to assert privileges “that may or may not belong to him does not provide a legal basis for Mr. Bannon’s refusal to comply” with the subpoena, Thompson wrote in his Oct. 15 letter.

In an Oct. 8 letter to Costello, he noted that the subpoena requests information that concerns “Bannon’s actions as a private citizen” regarding topics that are not protected by executive privilege. “Even if your client had been a senior aide to the President during the time period covered by the contemplated testimony, which he was most assuredly not, he is not permitted by law to the type of immunity you suggest that Mr. Trump has requested he assert,” Thompson wrote.

Bannon left his job as a top White House adviser to Trump in 2017.

Charles Cooper, who has advised Republican presidential advisers in the past on claiming immunity from congressional inquiries, said Monday that “Bannon’s claim is utterly without merit.”

“He cannot legally defend defiance of a subpoena” in part because he was not an official adviser to the president during the period of time in question, according to Cooper. “The issues here are multilayered,” he said, noting that the authority to invoke executive privilege lies with the incumbent president, not his predecessor.

“The overarching point is that the president’s immunity from congressional subpoena extends only to his closest Oval Office advisers, and Bannon clearly did not qualify at the time of his communications with President Trump about the election,” Cooper said.

However, a Minnesota lawyer observing the case, Marshall Tanick, said Monday that executive privilege is intended “to encourage unfettered communications by the president with others during his time in office. To be effective, it must extend to those senior advisers and confidants with whom he communicates and remain in effect after the term of office ends.”

In his most recent letter, Thompson emphasized that much of the information sought from Bannon was about his discussions of Jan. 6 with members of Congress, Trump campaign officials and “other private parties . . . that could not conceivably be barred by a privilege claim.”

Bannon’s status as a private citizen and his flat refusal to cooperate made him an obvious target for the committee hoping to set an example for other witnesses, according to legal experts.

“Bannon is in the weakest position to refuse compliance with the subpoena as a private citizen — he has the most tangential claim to being protected by executive privilege,” said Jonathan Turley, a professor at George Washington University who has written about the protection of White House documents and previously argued that Democrats’ impeachment efforts against Trump were a misguided use of congressional power.

Even for former Trump officials, Turley added, “Congress has an advantage in seeking testimony, but for private citizens like Bannon, it’s difficult to see a viable legal basis for simply refusing to comply with an otherwise valid subpoena.”

Panel members have made clear they have little patience for anything they view as a stalling tactic or attempt to avoid scrutiny.

“This potential criminal contempt referral — or will-be criminal contempt referral for Steve Bannon — is the first shot over the bow,” committee member Adam Kinzinger (R-Ill.) said on CNN’s “State of the Union” on Sunday. “It says to anybody else coming in front of the committee, ‘Don’t think that you’re going to be able to just kind of walk away and we’re going to forget about you. We’re not.’ ”

In response to a question from a reporter, Biden said Friday that he hoped the Justice Department would decide to prosecute after receiving the referral. His statement drew criticism from Republicans who argued it showed the investigation was being politicized. The department quickly issued a statement saying it reviews any referral without regard to political pressure.

“The Department of Justice will make its own independent decisions in all prosecutions based solely on the facts and the law. Period. Full stop,” Justice Department spokesman Anthony Coley said in a statement Friday.

While the president and the committee support the idea of moving quickly on a criminal referral, some outside experts are dubious.

“It’s not going to shorten the process. If anything, it’s going to go a long game,” said Stanley Brand, a former House general counsel. “There’s a lot of ways that he goes to trial and he forces the committee or the Department of Justice to prove each and every element of a congressional contempt beyond a reasonable doubt.” Others noted the panel is facing the potential political deadline of the 2022 midterm elections, after which Democrats could lose control of the House.

Bannon is considered a key witness for the committee because he had conversations with Trump in the weeks leading up to Jan. 6 and held a meeting with Trump allies on Jan. 5 at the Willard Hotel. That day, Bannon said on his podcast that “all hell is going to break loose tomorrow.”

Trump has mentioned executive privilege in comments to reporters but formally asserted it and other privileges only this month in attempting to block the National Archives from releasing 45 specific documents requested by the committee.

As a sitting president, Biden controls the invocation of executive privilege. He rejected Trump’s assertion that privilege protected release of the documents. Biden’s White House counsel, Dana Remus, wrote the head of the National Archives that “President Biden has determined that an assertion of executive privilege is not in the best interests of the United States, and therefore is not justified as to any of the documents.”