Former national security adviser John Bolton was "personally involved in many of the events, meetings and conversations" at the heart of the House impeachment inquiry "as well as many relevant meetings and conversations that have not yet been discussed" publicly, his lawyer revealed Friday.

Bolton's attorney, Charles Cooper, made the disclosure to the House's general counsel in an effort to explain why his client needs a court order to be able to testify in the impeachment inquiry into President Donald Trump.

Cooper said both Bolton and his deputy, Charles Kupperman, have information concerning "national security and foreign affairs," and Bolton has information that hasn't been touched on publicly to date.

Bolton "was personally involved in many of the events, meetings, and conversations about which you have already received testimony, as well as many relevant meetings and conversations that have not yet been discussed in the testimonies thus far," Cooper wrote.

Bolton, who stepped down in September, did not appear for a scheduled deposition on Thursday because he and Kupperman are seeking a judge’s ruling on whether they're bound by the White House's directive not to appear. The White House says the pair have "absolute testimonial immunity," Cooper noted.

Kupperman filed suit days before he was scheduled to give closed-door testimony last month, asking a federal judge to determine whether he is required to testify in the impeachment inquiry. The lawsuit said Kupperman was in an untenable position because the House was directing to him appear and White House lawyers were telling him not to do so.

The judge in the case scheduled a hearing for Dec. 10, which the House argued was too long to wait. The committees withdrew their subpoena against Kupperman earlier this week, and House Intelligence Committee Chairman Adam Schiff, D-Calif., told reporters they were prepared to move ahead without testimony from Bolton and Kupperman.

"We are not going to delay our work,” Schiff said. "That would merely allow these witnesses and the White House to succeed with their goal, which is to delay, deny, obstruct."

Schiff suggested the pair should be bound by whatever another judge decides on executive privilege claims involving former White House lawyer Don McGahn. The House Judiciary Committee has been seeking to question McGahn about allegations in the Mueller report that Trump had directed him to fire the special counsel.

In his letter, Cooper said Bolton and Kupperman's cases are different from McGahn's. The ex-White House lawyer "was not performing sensitive national security or foreign affairs functions," and the judge's ruling in that case would not apply to his clients, the lawyer wrote.

Cooper added, "We are dismayed that the committees have chosen not to join us" in seeking a resolution from the courts. "Dr. Kupperman stands ready, as does Ambassador Bolton, to testify if the Judiciary resolves the conflict in favor of the Legislative Branch's position respecting such authority," he wrote.

"If the House chooses not to pursue through subpoena the testimony of Dr. Kupperman and Ambassador Bolton, let the record be clear: That is the House’s decision," he wrote.