Former national security adviser John Bolton likely wouldn’t be helpful as a Senate impeachment witness because he “know[s] nothing” on the matter, President Trump said this week.

“[Bolton] would know nothing about what we’re talking about,” Trump said Tuesday when asked if he would be comfortable with his former national security adviser testifying on events relating to the Ukraine probe.

“As you know, the Ukrainian government came out with a very strong statement, no pressure, no anything, and this from the boss,” Trump went on to say, adding, “That’s from the president of Ukraine. The foreign minister came out with a statement that was equally as strong.”

Bolton, who went from Trump ally to foe after clashing with administration officials over the withholding of aid to Ukraine, said in a statement Monday that he would testify if subpoenaed during the Senate’s impeachment trial.

“The House has concluded its constitutional responsibility by adopting articles of impeachment related to the Ukraine matter. It now falls to the Senate to fulfill its constitutional obligation to try impeachments, and it does not appear possible that a final judicial resolution of the still-unanswered constitutional questions can be obtained before the Senate acts,” Bolton wrote.

“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. I have concluded that, if the Senate issues a subpoena for my testimony, I am prepared to testify.”

Asked by reporters about Bolton’s newest statement, Trump responded, “That’s going to be up to the lawyers. It’ll be up to the Senate, and we’ll see how they feel.”

Trump was impeached by the House in December on charges of abuse of power and obstruction of Congress. The charges stemmed from a July 25 phone call with Ukrainian President Volodymyr Zelensky, in which Trump asked the leader to open an investigation into 2020 Democratic presidential front-runner Joe Biden and his son Hunter in exchange for much-needed military aid and an already promised White House meeting.

House Democrats allege that Trump abused his power by asking for a foreign power to investigate a domestic political rival while withholding critical aid from a US ally.