President Donald Trump has reportedly floated firing administration officials who have testified in the House impeachment investigation into Trump’s Ukraine scheme.

CNN reported on Monday night that Trump, ever fixated with loyalty, has suggested having Lt. Col. Alexander Vindman, a Pentagon official who currently serves on the National Security Council, and Ambassador Bill Taylor fired after both provided key testimony on Trump’s attempt to manipulate U.S. relations with Ukraine for political gain.

Unnamed sources told CNN that White House aides warned Trump against forcing out the witnesses, advising that doing so would be seen as retaliation.

As an alternative, the aides are reportedly considering having witnesses with temporary posts at the White House, such as Vindman, removed from their posts and returned to their agencies.

National Security Adviser Robert O’Brien told CBS News’ “Face the Nation” host Margaret Brennan last week that Vindman will eventually be sent back to the Pentagon as part of the White House’s “streamlining” efforts. He denied any retaliation against Vindman.