Trump and O’Donnell have bickered for years, dating back to their TV days. O’Donnell identifies as a liberal and railed against Trump’s policy views during the campaign and supported Democratic nominee Hillary Clinton.

Trump unexpectedly fired FBI Director James Comey this week, citing the investigation into Clinton’s emails last year.

Trump said he acted based on the recommendations of Attorney General Jeff Sessions and Deputy Attorney General Rod Rosenstein, who found that Comey improperly moved to “usurp” the attorney general’s authority and decided not to prosecute Clinton.

“I have received the attached letters from the attorney general and deputy attorney general of the United States recommending your dismissal as the director of the Federal Bureau of Investigation,” Trump said in a letter to Comey. “I have accepted their recommendation and you are hereby terminated and removed from office, effective immediately.”

“While I greatly appreciate you informing me, on three separate occasions, that I am not under investigation, I nevertheless concur with the judgment of the Department of Justice that you are not able to effectively lead the bureau,” Trump said. “It is essential that we find new leadership for the FBI that restores public trust and confidence in its vital law enforcement mission. I wish you the best of luck in your future endeavors.”

The Trump administration immediately began a search for Comey’s successor. Acting leader, FBI Deputy Director Andrew McCabe has been floated as a possible replacement.

According to a NBC producer, O’Donnell responded to Trump’s tweet by saying: “It’s a clear indication of his seriously declining mental health…this is no joke.”