WASHINGTON (CNN) - Former national security adviser John Bolton has "personal knowledge" of relevant meetings and conversations "that have not yet been discussed in testimonies thus far" as part of the impeachment inquiry into President Donald Trump, but he is still refusing to testify until a federal judge rules in an ongoing legal fight between House committees and the White House, according to his lawyer.
Bolton's lawyer, Charles Cooper, wrote a letter to lawmakers Friday in which he teased the idea that his client could offer new details related to the impeachment probe, as well as additional context about events that have been described in other witness testimony.
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," the letter reads.
But despite underscoring Bolton's value as a potential witness, Cooper makes clear that his client is unwilling to testify until the court reaches a decision in the legal fight over claims of immunity for White House officials.
Trump's former national security adviser is at the center of several key events related to the investigation. Those include suggestions that he had raised concerns about the President and Ukraine, calling efforts by some top officials to help push for investigations into former Vice President Joe Biden and matters related to the 2016 election a "drug deal," according to testimony last month from former top White House Russia adviser Fiona Hill.
Several witnesses in the probe have already testified that Bolton had concerns about Trump's dealings with Ukraine and encouraged his staff to sound the alarm about potentially illegal actions by the President's personal lawyer, Rudy Giuliani.
The House committees conducting the inquiry opted not to subpoena Bolton after his attorney threatened to fight such a move in court, according to a committee official, and, unsurprisingly, the former national security adviser was a no-show Thursday.
"We would welcome John Bolton's deposition and he did not appear as he was requested today. His counsel has informed us that unlike three other dedicated public servants who worked for him on the NSC and have complied with lawful subpoenas, Mr. Bolton would take us to court if we subpoenaed him," the official said in a statement provided to CNN.
"We regret Mr. Bolton's decision not to appear voluntarily, but we have no interest in allowing the Administration to play rope-a-dope with us in the courts for months. Rather, the White House instruction that he not appear will add to the evidence of the President's obstruction of Congress," they added.
One of the legal cases in question involves Bolton's former deputy, Dr. Charles Kupperman, who is also represented by Cooper.
Kupperman failed to appear under subpoena last week after filing a lawsuit asking a federal judge to determine if he was obligated to testify. Kupperman's subpoena was withdrawn Wednesday as House Democrats moved to avoid delays caused by court proceedings.
The House has instead suggested Kupperman abide by what is decided in a separate case that is further along: its lawsuit against Don McGahn to force the former White House counsel to testify.
McGahn's case is "much closer to resolution by the court than Dr. Kupperman's flawed suit," the House wrote to Cooper. "Unless your lawsuit was admittedly only for purposes of delay, and without a subpoena in force, the Committees expect that your client will voluntarily dismiss the complaint ... and be guided by the decision in McGahn."
A House Intelligence Committee official explained why the House withdrew the subpoena for Kupperman, noting the court process "would only result in delay."
"There is no proper basis for a witness to sue the Congress in court to oppose a duly authorized congressional subpoena," the official said. "Nevertheless, given the schedule of our impeachment hearings, a court process that leads to the dismissal of Dr. Kupperman's flawed lawsuit would only result in delay, so we have withdrawn his subpoena."
However, Cooper said in his letter Friday that even if a court decides McGahn can testify, such a holding would not automatically clear the way for either of his clients to do so.
Cooper said that unlike McGahn, who was not going to be asked about "sensitive national security or foreign affairs functions," his two clients would be talking about matters "at the heart of the Committee's impeachment inquiry" and that such testimony could arguably fall within the President's assertion of absolute testimonial immunity.
Cooper also pushed back against claims that the lawsuit is intended "to delay or otherwise obstruct the Committees' vital investigatory work," reiterating that both of his clients think it is important for the judiciary branch to weigh in on the issue.
If Bolton does ultimately end up testifying, sources close to him have told CNN that he will likely lay blame on several individuals who have come under scrutiny in the impeachment proceedings, including Giuliani, US Ambassador to the European Union Gordon Sondland and acting White House chief of staff Mick Mulvaney.
"He will say that Giuliani, Mulvaney and Sondland, to a degree, were being disloyal to the President," a source close to Bolton said. "John will say, 'I was the guardrail while Giuliani and Mulvaney were saying let Trump be Trump.' "
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