In this July 31, 2019, file photo, then-national security adviser John Bolton speaks to media at the White House in Washington. Bolton said he's "prepared to testify" in Senate impeachment trial if subpoenaed. Credit: Carolyn Kaster | AP

WASHINGTON — Former White House national security adviser John Bolton said Monday that he is “prepared to testify” if subpoenaed by the Senate in its impeachment trial of President Donald Trump, a surprise statement bolstering Democrats in a push for new witnesses.

Bolton, who left the White House in September, said that he has weighed the issues of executive privilege and that after “careful consideration and study” decided that he would comply with any subpoena from the Republican-led Senate.

Democrats are pressing to hear from Bolton and others who did not appear before the House in its impeachment inquiry. Senate Majority Leader Mitch McConnell, R-Kentucky, has publicly expressed resistance to calling new witnesses in the upcoming trial. Sen. Susan Collins, R-Maine, has said she’s open to witnesses, but that it is premature to decide now on them.

It’s unclear whether Bolton’s testimony would hurt or help the president. The two clashed while he was in the White House and offered differing versions of whether he resigned or was fired when he left office in September.

If Bolton were to appear, his testimony would give Congress and the public a highly anticipated, first-hand account from a Trump senior adviser who was present for key moments that have been described by others.

He’d almost certainly be asked, for instance, about a comment he was reported to have made to another White House adviser that he did not want to be “part of whatever drug deal” European Union ambassador Gordon Sondland and White House chief of staff Mick Mulvaney were “cooking up” as Trump pressured Ukraine to investigate Democrats.

That pressure, as Trump was withholding security aid to Ukraine, was at the heart of the inquiry in the House, which voted to impeach Trump on Dec. 18.

House Speaker Nancy Pelosi is stalling the transmission of House-passed articles of impeachment against Trump in a bid for witness testimony. Senate Democratic Leader Chuck Schumer has proposed calling several witnesses, including Bolton and Mulvaney, but McConnell has so far rejected Schumer’s terms.

It is uncertain when Pelosi will send the articles to the Senate. If she decides to do so in the coming days, a trial could start this week. Collins, who has largely declined to comment on impeachment citing her role as a juror, could be a key figure in determining the Senate process.

In an interview with Maine Public last week, she hit McConnell and leading Democrats for taking sides on removing Trump. Collins said in a Monday statement that Bolton “may certainly be” an appropriate witness, but that the Senate should follow procedures from the 1999 impeachment of President Bill Clinton, when witnesses weren’t determined until the trial began.

“It is difficult to decide in isolation what the full universe of witnesses should look like before we have even heard the opening statements from the House managers and the President’s Counsel,” Collins said.

Bolton’s willingness to testify averts a potential legal standoff over whether close aides to the president can be forced to appear before Congress. Trump and his lawyers have claimed that those aides should not have to testify, arguing that they have special immunity, or executive privilege, not to.

The issue remains undecided in the courts now that a federal judge dismissed last week a lawsuit from Bolton’s former deputy, Charles Kupperman, who had asked the court whether he had to comply with a House subpoena or follow a White House order that he not testify. U.S. District Judge Richard Leon dismissed the case as moot, noting that the House had withdrawn its subpoena for Kupperman and had said that it didn’t plan to reissue one.

BDN writer Michael Shepherd and Associated Press writer Hillel Italie contributed to this report.