Former White House national security adviser John Bolton said Monday he is willing to testify — if he is subpoenaed — in the Senate’s impeachment trial of President Donald Trump. Bolton issued a statement Monday 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,” Bolton said. “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.Bolton’s statement is likely to put new pressures from Democrats on Senate Majority Leader Mitch McConnell to allow witnesses in the Senate trial, which Senate Democratic Leader Chuck Schumer and Democratic House leaders have pushed for. So far, McConnell has resisted Schumer’s calls to have witnesses in the Senate trial, instead calling for an agreement on the rules of the Senate trial that would put off the question of witnesses until later on.Bolton left a message with McConnell before he put out the statement to give him a heads up that it was coming, according to a source familiar with the matter. The White House was not informed.Amid the Senate’s impasse, House Speaker Nancy Pelosi has yet to formally send the two impeachment articles to the Senate after the House passed them last month.Trump’s apparent frustration with impeachment trial simmers over holidays Pelosi had no advanced knowledge of Bolton’s statement, but a senior Democratic aide said Pelosi’s decision to withhold the articles played a role.”We would not have this development absent the speaker’s hold,” the senior Democratic aide said. “Another proof point that indicates the value of her strategy.”House Intelligence Chairman Adam Schiff, a California Democrat, sought Bolton’s testimony during the House’s impeachment investigation into Trump’s dealings with Ukraine. But Bolton’s former deputy, Charles Kupperman, filed a lawsuit after he was subpoenaed, arguing the White House was directing him not to testify and the courts should decide the issue. Instead, the House withdrew its subpoena of Kupperman and did not issue a subpoena for Bolton after his attorney indicated he would go the same route.Bolton and Kupperman are two of several witnesses that House Democrats sought whom Senate Democrats are now pushing for in the Senate trial, including acting chief of staff Mick Mulvaney and White House aide Rob Blair. The new statement comes after Bolton was both surprised and curious that he had not been subpoenaed by the House, according to the source familiar with the matter. There had been mounting criticism that he wanted to hold off on sharing what he knew about the withholding of aid to Ukraine for his book. It is unclear what specifically triggered him to put out this statement right now.It is unclear what Bolton will do if the White House tries to block his testimony, or parts of it, the source said. But the statement speaks for itself in that he is prepared to provide testimony.