Washington: Former National Security Adviser John Bolton said on Monday he is willing to testify if subpoenaed during President Donald Trump’s impeachment trial in the Senate.

“I have concluded that, if the Senate issues a subpoena for my testimony, I am prepared to testify,” Bolton said in a statement posted on his political action committee’s website.

Bolton’s pronouncement injects fresh drama into the trial, which has been delayed amid partisan squabbling over Democrats’ demand that key administration figures appear as witnesses.

The White House blocked many of those people, including Bolton, from testifying to the House during its impeachment inquiry into Trump’s attempt to pressure the Ukrainian government to investigate his political rivals.

Bolton’s move ratchets up pressure on Senate Majority Leader Mitch McConnell to agree to call witnesses during the trial, a commitment he has refused to make. McConnell has ripped the Senate’s Democratic leader Chuck Schumer’s call for testimony from four witnesses, including acting White House chief of Staff Mick Mulvaney and Bolton, as a “fishing expedition.”

Senate Democrats seized on the announcement.

“John Bolton should testify,” tweeted Senator Mark Warner, the top Democrat on the Senate Intelligence Committee.

A Senate Republican leadership aide said it would take 51 votes to issue a subpoena for Bolton’s testimony, an outcome that might be unlikely in the GOP-controlled chamber. The White House did not immediately respond to a request for comment.

Bolton could potentially offer explosive testimony about what Trump said privately during his effort to force Ukraine to probe former Vice President Joe Biden and his son, Hunter. He would be the most senior Trump White House aid to testify in impeachment proceedings.

Former National Security Council official Fiona Hill testified to the House that Bolton referred to the president’s personal attorney, Rudy Giuliani, as a “hand grenade who’s going to blow everybody up.” Giuliani has led a months-long effort to dig up dirt on the Bidens in Ukraine, work he has said he has done in his capacity as Trump’s private lawyer.

Bolton referred to the efforts to pressure Ukraine as a “drug deal” and said he would not get involved, Hill said.

In November, Bolton’s lawyer wrote in a letter filed in federal court that the former Trump adviser “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.”

Bolton had joined a lawsuit with Charles Kupperman, who worked on the National Security Council, and sued Trump and House Democrats in October seeking a ruling on whether the president’s order for him to ignore a House subpoena was legal. The House ultimately withdrew its subpoena, and the Justice Department said it wouldn’t go after Kupperman for flouting it, making the dispute moot, the judge decided.