Special counsel Robert Mueller has acquired a draft of an initial letter that President Donald Trump and a senior adviser drew up to justify the firing of former FBI director James Comey, the New York Times reported Friday.

A dozen administration officials told the newspaper that White House counsel Don McGahn blocked that letter, which was written with an assist from hardline policy adviser Stephen Miller, from being sent out because he was concerned that some of its arguments were problematic.

The Times did not report on the contents of the draft letter, but noted that it “appears to provide the clearest rationale that Mr. Trump had for firing Comey.”

One factor laid out in the letter was Trump’s irritation with Comey for not publicly declaring that the President wasn’t personally under investigation in the federal probe into Russia’s interference in the 2016 election, the Washington Post subsequently reported.

After his firing, Comey testified before Congress that he informed Trump privately on three separate occasions that he was not a subject of the FBI’s investigation. Ironically, it was Trump’s swift dismissal of his FBI director and his later comments about making the decision because of his irritation over the ongoing Russia investigation that prompted the FBI to open a probe into whether the President obstructed justice.

The Justice Department turned the letter over to Mueller in recent weeks, according to the report. Ty Cobb, one of Trump’s outside lawyers, declined to comment, telling the Times simply, “To the extent the special prosecutor is interested in these matters, we will be fully transparent with him.”

When Comey was abruptly fired in early May, the White House released letters from Attorney General Jeff Sessions and Deputy Attorney General Rod Rosenstein that recommended that Comey be dismissed for his handling of the probe into Hillary Clinton’s use of a private email server.

Trump undercut that explanation soon afterward by telling an NBC anchor—and, reportedly, visiting Russian diplomats—that he fired Comey to relieve pressure the federal investigation into Russia’s interference in the 2016 election was putting on him.

Mueller is investigating whether Trump obstructed justice by firing Comey, who initially led that probe as FBI director, and by reportedly asking Comey earlier in the year to quash an investigation into Michael Flynn, his former national security adviser.

Several people who reviewed the initial draft letter told the Post that it makes clear that Trump had set his plans to fire Comey in motion days before receiving recommendations from his top DOJ officials. The decision came during a weekend he spent at his golf club in Bedminster, New Jersey, where a handful of aides including Miller, his daughter Ivanka, and his son-in-law and senior adviser Jared Kushner were present, per the report.