The House Intelligence Committee may be interested in Trump's draft letter firing Comey

The ranking member of the House Intelligence Committee told CNN on Sunday that he believed a draft letter written by President Donald Trump in early May, in which he detailed the reasons why he wanted to fire then FBI director James Comey, could be "further evidence" of obstruction of justice if it indicated that Trump was firing Comey to stymie the FBI's Russia investigation.

Rep. Adam Schiff told CNN's Dana Bash that he had not personally seen the letter, which is in the possession of special counsel Robert Mueller, but indicated that he was interested in reviewing it.

"We wrote to the White House after the claim was made that the president had tapes of his discussions with Comey, to ask about anything memorializing any conversations with Comey," Schiff said.

He was referring to a tweet Trump posted three days after firing Comey, saying that "

Legal experts say the letter Mueller is reviewing is possibly the most critical piece of evidence in Mueller's obstruction-of-justice case since Comey's testimony before the Senate Intelligence Committee in June, because it can give prosecutors a direct window into Trump's thinking shortly before he fired Comey.

"The best way to prove someone's intent is through their own words and actions," former federal prosecutor Renato Mariotti told Business Insider in an interview Saturday. "Here, you have a letter that was written by Miller, at the direction of the president, that contains what the president's thoughts were at that time."

Though the letter's full contents remain unclear,The Washington Post reportedthat it focused on what was perhaps Trump's greatest frustration with Comey: that the FBI director did not publicly announce, when he was leading the bureau's probe, that Trump was not personally under investigation.

"It's problematic for Trump if he fired Comey because he did not take actions in the investigation that would benefit Trump personally," Mariotti said. "That makes Mueller's case stronger."

Schiff told CNN on Sunday that if Trump and Miller explicitly said that the president was firing Comey because of the Russia investigation, it would be "further evidence" of obstruction of justice.

"Certainly it's consistent, or would be consistent, with what the president himself admitted, and the fact that it's in such sharp contrast to what they initially said — that this was about [Comey's] handling of the Clinton email investigation — is further evidence of an attempt to conceal the real motives," he added.

Though the White House initially said that Trump fired Comey based entirely on Rosenstein's and Attorney General Jeff Sessions' recommendations, Trump later said he had already decided to fire Comey, and that Rosenstein's recommendation sealed the deal.

His explanation changed again later on, when he admitted to NBC News' Lester Holt that he had fired Comey because of "this Russia thing," and that he was going to dismiss the FBI director regardless of Rosenstein's input.