In the letter to Mueller, Trump's lawyers had contended that the Constitution gives the president the power to "terminate the inquiry, or even exercise his power to pardon", and that meant he could not illegally obstruct the investigation, the Times reported.
The letter, which was penned by Trump lawyers Jay Sekulow and John Dowd, appears to lay out the legal team's view of the extent of the president's power - and may foreshadow a coming subpoena battle between Mueller and Trump.
"Can you believe that with all of the made up, unsourced stories I get from the Fake News Media, together with the $10,000,000 Russian Witch Hunt (there is no Collusion), I now have my best Poll Numbers in a year".
The arguments parallel those that the president's attorneys have pressed publicly for months, even as quiet negotiations over whether Trump might agree to sit voluntarily for an interview have continued.
"In light of these voluntary offerings, your office clearly lacks the requisite need to personally interview the President", the letter argues. His statement implies that President Obama knew about the investigation of the Trump campaign, and it was his call whether to keep candidate Trump in the dark.
It argued that Mr Trump is the country's "chief law enforcement officer" and therefore claims of obstructing justice "would amount to him obstructing himself".
Sessions' move infuriated the president, who once reportedly mused about why he couldn't have "my guys" at the "Trump Justice Department" do his bidding.
According to the Times, the letter was hand-delivered to the special counsel's office in January and sets the stage for a potential subpoena fight. That includes $4.5 million spent by Mueller's team and another $5.5 million spent by the Justice Department on other expenditures attributable to the investigation. "Every action that the president took was taken with full constitutional authority pursuant to Article II of the United States Constitution", his lawyers wrote referring to the part of the Constitution that establishes the executive branch.
Lawyers for President Trump told special counsel Robert Mueller that he already has the information he needs from thousands of documents they provided, as well as from other testimony. Mr. Trump fired Comey on May 9, 2017. In fact, Donald Trump Jr. had accepted the meeting after being told the lawyer would provide dirt about Clinton. They have been trying to sway Mueller away from seeking a subpoena to force Trump to testify before a grand jury.