The House committee investigating the Jan. 6 attack on the U.S. Capitol formally issued its extraordinary subpoena o Donald Trump on Friday, demanding testimony from the former president who lawmakers say “personally orchestrated” a multi-part effort to overturn the results of the 2020 election.

The nine-member panel issued a letter to Trump's lawyers saying he must testify, either at the Capitol or by videoconference, “beginning on or about” Nov. 14 and continuing for multiple days if necessary. The letter also outlined a request for a series of corresponding documents, including personal communications between Trump and members of Congress as well as extremist groups.

“We recognize that a subpoena to a former president is a significant and historic action," Chairman Bennie Thompson and Vice Chair Liz Cheney wrote in the letter to Trump. “We do not take this action lightly.”

The panel rooted its action in history, listing past presidents from John Quincy Adams to Gerald Ford who testified before Congress after leaving office -- and noting that even sitting presidents have responded to congressional subpoenas.

It is unclear how Trump and his legal team will respond. He could comply or negotiate with the committee, announce he will defy the subpoena or ignore it altogether. He could also go to court and try to stop it.

A request for comment from Trump's spokesperson was not immediately returned.

The subpoena is the latest and most striking escalation in the House committee’s 15-month investigation of the deadly Jan. 6, 2021, insurrection, bringing members of the panel into direct conflict with the man they have investigated from afar through the testimony of aides, allies and associates.

The committee writes in its letter that it has assembled “overwhelming evidence” that Trump “personally orchestrated” an effort to overturn his defeat in the 2020 election, including by spreading false allegations of widespread voter fraud, “attempting to corrupt” the Justice Department and pressuring state officials, members of Congress and his vice president to try to change the results.

But lawmakers say key details about what Trump was doing and saying during the siege remain unknown. According to the committee, the only person who can fill the gaps is Trump himself.

The panel - comprised of seven Democrats and two Republicans - approved the subpoena for Trump in a surprise vote last week. Every member voted in support.

The day after, Trump posted a lengthy memo on Truth Social, his social media website, repeating his false claims of widespread election fraud and expressing his “anger, disappointment and complaint” that the committee wasn’t investigating his objections. He made no mention of the subpoena.

The subpoena calls for testimony about his dealings with several former Trump aides and associates who have asserted their Fifth Amendment rights against self-incrimination to the committee, including Roger Stone, Michael Flynn, John Eastman, Jeffrey Clark and Kelli Ward.

The committee makes 19 requests for documents and communication -- including specific requests for any messages Trump sent on the encrypted messaging app Signal “or any other means” to members of Congress and others about the stunning events of Jan. 6.

The scope of the committee's request is expansive-- pursuing documents from Sept. 1, 2020, two months before the election, to the present on the president’s communications with the Oath Keepers, Proud Boys and other extremist groups -- as the panel compiles a record of the run-up to the Capitol attack and then the aftermath.

There is little legal advantage for Trump to cooperate with the committee as he already faces other civil and criminal legal battles in various jurisdictions, including over his family business in New York and the handling of presidential records at his Mar-a-Lago estate in Florida.

But there is ample precedent for Congress seeking testimony from former presidents. Over the past century and a half, at least six current and former presidents have testified on Capitol Hill, including John Tyler and John Quincy Adams after both were subpoenaed in 1848.

If Trump refuses to comply with the subpoena, the panel will have to weigh the practical and political implications of holding him in contempt of Congress.

“That’s a bridge we cross if we have to get there,” Rep. Adam Kinzinger, a Republican member of the committee, told ABC on Sunday. “He’s made it clear he has nothing to hide, is what he says. So, he should come in.”

If the full House voted to recommend a contempt charge against Trump, the Justice Department would then review the case and decide any further step.

Other witnesses have faced legal consequences for defying the committee, including close Trump ally Steve Bannon, who was convicted of contempt in July and was sentenced Friday to four months behind bars. But holding a former president in contempt would be another matter, truly exceptional.

The subpoena to Trump comes as the committee is looking to wrap up its investigative work and compile a final, comprehensive report that will be published by the end of the year. Investigators have interviewed more than 1,000 witnesses, including many of Trump’s top White House aides, and obtained tens of thousands of pages of documents since the committee was formed in July 2021.

But the panel is authorized only through this Congress, which ends on Jan. 3. That means members have only a few short months - amid a hectic lame-duck legislative period after the midterm elections - to refine their historical record of the worst attack on the Capitol in two centuries. Whether that will include the testimony from the 45th president of the United States remains to be seen.

“It’s hard for me to imagine any American citizen being accused of essentially trying to overthrow his or her own government who wouldn’t welcome the opportunity to come forward and to testify,” Rep. Jamie Raskin, a Democrat on the committee, told reporters last week.