When President Donald J. Trump fired James B. Comey as F.B.I. director on May 9, the White House made public a memorandum from Rod J. Rosenstein, the deputy attorney general, recommending the dismissal. The firing elicited a strong reaction due to the F.B.I.’s investigation of contacts between members of the Trump campaign and Russia.

The press made a big deal over the memo, but it’s now come to light that the Rosenstein letter was not the original letter drafted in the days before the firing. It is being reported that an original draft of a letter written by President Trump and top political aide Stephen Miller has been unearthed which explains the president’s true rationale for why he planned to dismiss the director.

The special counsel, Robert S. Mueller III, has obtained the letter, but no one knows what it says. What is being reported about the letter is that it wasn’t sent to Comey because Donald F. McGahn II, the White House counsel, was of the opinion that some of its contents were problematic, according to interviews with a dozen administration officials and others briefed on the matter, reports The Hill.

McGahn successfully blocked the president from sending Comey the letter, and a different letter, written by the Deputy Attorney General Rod J. Rosenstein, was sent to fire the F.B.I. director, instead. That letter was made public in The New York Times.

Rosenstein, who served as the United States attorney in Maryland under Presidents George W. Bush and Barack Obama, is known to be a by-the-book, nonpartisan prosecutor. In his memo, he focused on the continuing fallout of Comey’s handling of the investigation into Hillary Clinton’s use of a private email server while she was secretary of state.

Rosenstein criticized Comey for overstepping his role and noted that he appeared to have taken a partisan interest in the Clinton case.

“The Director was wrong to usurp the Attorney General’s authority on July 5, 2016, and announce his conclusion that the case should be closed without prosecution. It is not the function of the Director to make such an announcement. At most, the Director should have said the F.B.I. had completed its investigation and presented its findings to federal prosecutors,” wrote Rosenstein, as he laid out the rationale for firing Comey.

Rosenstein went on to blast Comey for the press conference he held on July 6, 2016, when the F.B.I. director announced, “Our judgment is that no reasonable prosecutor would bring such a case (against Hillary Clinton),” after a lengthy recap of the investigation.

“Compounding the error, the Director ignored another longstanding principle: We do not hold press conferences to release derogatory information about the subject of a declined criminal investigation,” wrote Rosenstein, adding, “The Director laid out his version of the facts for the news media as if it were a closing argument, but without a trial. It is a textbook example of what federal prosecutors and agents are taught not to do.”

Rosenstein also cited a letter Comey sent to Congress on Oct. 28, 2016, in which the director cast his decision as a choice between whether he would “speak” about the decision to investigate the newly-discovered email messages or “conceal” it.

“‘Conceal’ is a loaded term that misstates the issue,” wrote Rosenstein. “When federal agents and prosecutors quietly open a criminal investigation, we are not concealing anything; we are simply following the longstanding policy that we refrain from publicizing non-public information. In that context, silence is not concealment.”

On Friday, the Justice Department provided Mueller with the unpublished draft letter detailing President Trump’s rationale for firing Comey as he conducts his ever-widening investigation into Russian interference in the election, including whether the president obstructed justice by firing Comey, who was previously in charge of the probe.

It is unknown how much of the rationale in the original letter focused on the Russia investigation. Shortly after Comey’s May 9 dismissal, the president told NBC’s Lester Holt that the probe had been on his mind when he made the decision to fire the FBI director.

“Regardless of recommendation, I was going to fire Comey,” Trump said during an interview on “NBC Nightly News,” adding, “There was no good time to do it.”

He told Holt, “And, in fact, when I decided to just do it, I said to myself, ‘You know, this Russia thing with Trump and Russia is a made-up story.’”

Miller, a former aide to Attorney General Jeff Sessions when he was in the Senate, reportedly drafted the letter at President Trump’s request during a weekend in May at the president’s Bedminster, N.J., golf club.

During that same weekend, Sessions and Rosenstein were also coming up with reasons to dismiss Comey, according to the Times.

The firing came after Comey had just given testimony before the Senate Judiciary Committee in which he said that it made him “mildly nauseous” to think his actions during the election might have impacted the outcome.

Comey had declared that there would be no charges against Clinton over her secret server before later alerting Congress that the FBI was examining new evidence 11 days before the election. Clinton has said that Comey’s letter to lawmakers is one of the reasons she lost the presidency, which is probably more factual than saying that the Russians had anything to do with it.

Comey’s congressional testimony reportedly added to Rosenstein and Sessions’ concerns that the famously independent-minded director was overstepping the authority of his role.

The May 9 dismissal nevertheless set off a firestorm in Washington and led to the appointment of Mueller, which, according to Comey himself, was his goal all along.