President Donald Trump signaled in an interview aired Friday that he would seek to block key witnesses from testifying in the Senate’s impeachment trial, including former National Security Adviser John Bolton, former Energy Secretary Rick Perry, Secretary of State Mike Pompeo and White House chief of staff Mick Mulvaney.

Trump ordered the men, and several other witnesses, not to cooperate with the House of Representatives’ impeachment inquiry about his pressure campaign on Ukraine to produce political dirt against Democrats.

Now, as House Speaker Nancy Pelosi (D-CA) prepares to transmit two articles of impeachment to the Senate for an impeachment trial, Trump implied he would seek to do the same in that chamber.

Asked by Fox News host Laura Ingraham if he would invoke executive privilege in an attempt to prevent Bolton from testifying, Trump said “I think you have to, for the sake of the office.”

Bolton witnessed several attempts by Trump administration officials to pressure Ukraine to do the President’s political bidding.

At one point, referring to the EU ambassador and the White House chief of staff, Bolton reportedly told a deputy “I am not part of whatever drug deal [Gordon] Sondland and [Mick] Mulvaney are cooking up.”

After a judge dismissed his lawsuit seeking an answer on whether he was obliged to testify, Bolton announced last week that he would testify if subpoenaed.

Trump similarly suggested Friday he would seek to prevent potential testimony from Pompeo, Mulvaney and Perry.

“I would love everybody to testify,” he said. “I would like Mick to testify, I like Mike Pompeo to testify. I like Rick Perry to testify. I want everybody. But there are things that you can’t do from the standpoint of executive privilege.”

“You have to maintain that,” Trump continued. “So we’ll see where it all goes. But especially a national security adviser, you can’t have him explaining all of your statements about national security concerning Russia, China, North Korea, everything. You just can’t do that.”

A few GOP senators have hinted that they would be open to hearing witnesses later on in the Senate trial, but that hasn’t reassured Democrats; Pelosi has withheld the articles of impeachment from the Senate for weeks in an attempt to build political pressure on Senate Republicans to allow witnesses that were not part of the House’s hearings to testify.