John Bolton
John Bolton Reuters

Former White House national security adviser John Bolton said on Monday he is willing to testify, if he is subpoenaed, in the Senate's impeachment trial of President Donald Trump, CNN reports.

Bolton issued a statement after the courts did not rule whether he would be compelled to testify during the House's impeachment proceedings, saying he was trying to meet his "obligations both as a citizen and as former national security adviser."

"Accordingly, since my testimony is once again at issue, I have had to resolve the serious competing issues as best I could, based on careful consideration and study," he said in the statement. "I have concluded that, if the Senate issues a subpoena for my testimony, I am prepared to testify."

Bolton is potentially a crucial witness, as he had firsthand knowledge of many of the events that formed the House's impeachment of the President over his dealings with Ukraine.

The House sought his testimony but ultimately never subpoenaed Bolton, and Democrats withdrew their subpoena for his former deputy after it was challenged in court, as Democrats wanted to move forward with their impeachment probe and not wait for the court's decision.

Reports later said Bolton would be willing to testify before Congress in the impeachment investigations but only if a court rules on a congressional subpoena.

Senate Democratic leader Chuck Schumer proposed last month that at least four witnesses, including Bolton and acting White House Chief of Staff Mick Mulvaney, be subpoenaed to testify in the impeachment trial.

Responding to Bolton’s statement on Monday, Schumer said, "It is now up to four Senate Republicans to support bringing in Mr. Bolton, and the other three witnesses, as well as the key documents we have requested to ensure all the evidence is presented at the onset of a Senate trial."

"Given that Mr. Bolton's lawyers have stated he has new relevant information to share, if any Senate Republican opposes issuing subpoenas to the four witnesses and documents we have requested they would make absolutely clear they are participating in a cover up," added Schumer.

Bolton's statement is unlikely to change Senate Majority Leader Mitch McConnell's strategy over Trump's impeachment trial, multiple GOP sources familiar with the matter said, according to CNN.

McConnell has rejected Democratic demands to require that the ground rules of the trial include testimony of Bolton and three other witnesses, along with documents withheld by the White House. He says such decisions about witnesses and documents should be made after opening arguments, though Democrats fear that's an attempt to prevent any witnesses from testifying at all.

Ultimately, issuing a subpoena for Bolton would require 51 votes in the Senate, meaning at least four Republicans would have to join 47 Democrats.

Meanwhile, House Speaker Nancy Pelosi has yet to formally send the two impeachment articles to the Senate after the House passed them last month.

Until the House formally sends the articles, McConnell has said the trial will not start, but he's dismissed the idea that Democrats can enact any concessions by withholding the articles.

On Sunday, Senate Judiciary Committee Chairman Lindsey Graham (R-SC) said that if the House does not submit the articles of impeachment to the Senate this week, he will seek to change the impeachment rules so the Senate can proceed to a trial without them.