WASHINGTON — Former national security adviser John Bolton is willing to defy the White House and testify in the House impeachment inquiry about his alarm at the Ukraine pressure campaign if a federal court clears the way, according to people familiar with his views.
Bolton could be a powerful witness for Democrats: Top State Department and national security officials have already testified that he was deeply concerned about efforts by President Donald Trump and his allies to push Ukraine to open investigations into the president’s political rivals while the Trump administration held up military aid to that country.
The former national security adviser, who abruptly left his post in September, is expected to confirm their statements and describe his conversations with Trump, according to the people, who spoke on the condition of anonymity because of the ongoing inquiry.
However, Bolton, a longtime GOP foreign policy adviser, does not want to comply with the Democratic inquiry without a court ruling on the ongoing constitutional dispute between the Trump administration and Congress, the people said.
It remains unclear how quickly that could happen — and whether it would be in time for Bolton to be called as a witness in the public House impeachment hearings, which are scheduled to begin next week. On Wednesday, House Democrats said they are awaiting a key test case involving former White House counsel Donald McGahn, in which a district-court decision could come by the end of this month.
An attorney for Bolton declined to comment.
Bolton is considered a high-value witness in part because, as national security adviser, he would have spoken directly with the president about US foreign policy objectives in Ukraine.
His testimony is expected to be ‘‘damaging’’ to Trump, according to a person familiar with the matter.
But there is a major obstacle facing Democrats hoping to secure Bolton as a star witness: the court battle over congressional subpoenas will probably go to the Supreme Court and spill into next year.
While other officials have complied with requests to participate in the impeachment inquiry without such a judicial order, Bolton is not willing to do so, the people said.
House Democrats requested Bolton’s appearance at a closed-door deposition Friday, but he is not expected to appear. He has not been issued a subpoena.
However, the former national security adviser, who repeatedly tussled with Trump on foreign policy, is closely aligned with National Security Council aides who have already testified about his concerns, including former Russian affairs director Fiona Hill and Ukraine expert Alexander Vindman.
Hill told lawmakers that Bolton erupted after a key White House meeting on July 10 in which Sondland pressed Ukrainian officials to open investigations into former vice president Joe Biden and the 2016 campaign, equating the discussions to a ‘‘drug deal.’’
Bolton directed Hill to report what she had witnessed to John Eisenberg, the top lawyer for the National Security Council. Vindman also reported the episode to Eisenberg.
Bolton is expected to corroborate their testimony that he was aghast that US military aid was being held back as the president and his allies were pressuring Ukraine to open investigations that could be damaging to Democrats, according to the people familiar with his views.
However, the people note that Bolton also has an expansive view of presidential power. As a result, it is unclear whether he would testify that Trump overstepped his constitutional authority in his dealings with Ukraine.
Separately, William Taylor Jr., the acting ambassador to Ukraine, testified that Bolton was ‘‘very sympathetic’’ when he expressed concerns to the then-national security adviser that the aid was being withheld, according to a transcript released Wednesday.
Bolton recommended that Taylor send a ‘‘first person’’ cable to Secretary of State Mike Pompeo about his concerns, noting that such cables are rare and would be bound to get attention, Taylor told lawmakers.
Taylor also testified that other State Department officials had told him that Bolton was working to get the aid money for Ukraine released by returning authority over the funds to the secretaries of state and defense and the CIA director.
Now the battle will hinge on getting Bolton to narrate his version of events.
The White House has asserted a broad claim that current or past senior advisers such as Bolton have ‘‘absolute immunity’’ from providing testimony to lawmakers, part of broad resistance by the Trump administration of congressional oversight.
That assertion is now being tested in the courts.
Last month, Charles Kupperman, who served as a deputy to Bolton at the National Security Council, filed a lawsuit seeking a judicial ruling on whether he should comply with a subpoena from House Democrats or follow instructions from the White House not to appear. Kupperman’s attorney, Charles Cooper, also represents Bolton.
‘‘It would not be appropriate for a private citizen, like Dr. Kupperman, to unilaterally resolve this momentous constitutional dispute between the two political branches of our government,’’ Cooper wrote in a letter to House committee chairs.
In a court hearing last week, Cooper made clear that if Bolton is subpoenaed, he would probably join Kupperman in the lawsuit.
At Kupperman’s request, US District Judge Richard Leon in Washington fast-tracked the case, ordering that final arguments be held Dec. 10.
But on Wednesday afternoon, the House withdrew its subpoena of Kupperman and asked for the suit to be dropped.
House lawyers said that in the interest of speed, they would rely on another case that is further along in judicial proceedings — one involving a subpoena to McGahn, whose testimony was first sought in April after the release of special counsel Robert S. Mueller III’s report.
That case raises similar issues of whether the White House can bar high-ranking administration officials from testifying.
US District Judge Kentanji Brown Jackson in Washington heard oral arguments in the McGahn case last week and said she would probably issue an opinion before the end of November.
At the hearing, Jackson expressed skepticism about the Trump administration’s claim that Congress cannot compel the former White House counsel and top presidential aides to testify. She called it a ‘‘peculiar’’ argument that threatens to upset the Constitution’s system of checks and balances.