THE man leading the probe into Donald Trump’s alleged links with Russia has obtained a draft letter that could change everything.

Special counsel Robert Mueller’s team of investigators is in possession of a letter drafted by President Donald Trump and an aide, but never sent, that lays out a rationale for firing FBI Director James Comey, according to a person familiar with the investigation.

The letter was written in the days before the May 9 firing of Comey, but was held after objections from the president’s lawyer and others, according to two other people familiar with the process who were not authorised to discuss it publicly and spoke on condition of anonymity.

On that day, the White House released a different letter announcing Comey’s firing, one signed by Deputy Attorney-General Attorney Rod Rosenstein that cited the handling of the Hillary Clinton email investigation as a basis for Comey’s dismissal.

Trump had been fuming about Comey for weeks, upset that he would not say publicly that the president was not under investigation, which Trump said Comey had assured him privately.

That was in the earlier letter and was part of the president’s rationale for firing Comey. It was later excised — only to be partially restored in the final letter at Trump’s behest.

The earlier letter could serve as key evidence to Mueller’s team, which is now investigating whether Trump fired Comey to impede the FBI investigation into his campaign associates’ ties to Russia.

The White House has said Trump was acting on the Justice Department’s recommendation when he fired Comey, though the president said in a television interview days later that he was thinking of “the Russia thing” when he made the move and had planned to fire “regardless of recommendation.”

The new letter, which was first reported by The New York Times, could provide additional context on Trump’s thinking and motive as he prepared to oust Comey. The Justice Department turned the letter over to Mueller’s team, according to a person who was not authorised to publicly discuss the situation and spoke on condition of anonymity. A statement from the Justice Department said the department had been fully cooperative with Mueller’s investigation and would continue to do so.

One week after Comey was fired, Rosenstein appointed Mueller as special counsel to oversee an investigation into potential co-ordination between the Trump campaign and Russia. That investigation, which had been overseen by Comey, is also looking into the financial dealings of several Trump associates. During a May weekend at the president’s New Jersey golf club, Trump asked White House aide Stephen Miller to draft a letter outlining a case for Comey’s firing, according to two people familiar with the situation.

But the letter, which contained a rationale for the dismissal, was not sent after White House counsel Don McGahn objected, thinking some of its contents were problematic, according to one of the people familiar with the letter.