Donald Trump on Saturday evening sent out a tweet knocking former White House Counsel Don McGahn, who served under the president for nearly two years.

“I was NOT going to fire Bob Mueller, and did not fire Bob Mueller. In fact, he was allowed to finish his Report with unprecedented help from the Trump Administration,” Trump wrote, referencing allegations that he ordered McGahn to fire the special counsel in an attempt to obstruct justice. “Actually, lawyer Don McGahn had a much better chance of being fired than Mueller. Never a big fan!”

The tweet came in the wake of a Wall Street Journal article on Friday, which found that McGahn had rebuffed a request from the White House last month to put out a public statement asserting that he did not think Trump’s order to fire the special counsel amounted to obstructing justice. The New York Times further reported that Trump asked White House officials to reach out to McGahn with the request. According to the Times, Trump became angry when McGahn twice declined the request, seeing it as an act of disloyalty.

The Mueller report revealed that, over the course of extensive interviews, McGahn told investigators that he refused Trump’s orders to fire the special counsel and to put out a false public statement denying that such a conversation ever took place. However, the Washington Post reports that McGahn told the special counsel’s office that he did not think Trump’s actions were an obstruction of justice. McGahn would nevertheless likely be a key witness in a potential obstruction of justice case against the president.

The House Judiciary Committee issued a subpoena to McGahn in late April seeking documents related to the testimony he gave to the special counsel. The White House blocked the subpoena, citing “significant Executive Branch confidentiality interests and executive privilege.” McGahn’s lawyer, Bill Burck, also sent a letter to the committee declining to comply with the subpoena. House Judiciary Chairman Rep. Jerry Nadler on Tuesday threatened to hold McGahn in contempt.