But she said Mr Trump will not take that step in order to ensure a "swift and thorough examination of the facts" related to Mr Comey's sacking and the multiple investigations into Russia's election meddling.
Comey is scheduled to testify before the Senate Intelligence Committee at an open hearing on Thursday.
Trump tweeted on May 12: "James Comey better hope that there are no "tapes" of our conversations before he starts leaking to the press!"
Lawmakers in both parties have urged Trump to allow Comey to testify publicly.
Most major USA television networks plan to carry the event live.
Trump told NBC News he fired Comey in part because of the "Russia thing", which he called a "made-up story".
So perhaps unsurprisingly, toward the end of last week, Trump's aides floated the possibility that they could try to block Comey's testimony with an assertion of executive privilege - a legal argument presidents have used to shield activities or documents from congressional scrutiny.
It has been reported that Comey plans to talk about conversations in which Trump pressured him to drop his investigation into former national security advisor Mike Flynn, who was sacked for failing to disclose conversations with Russian officials.
The White House had floated the idea that Trump could invoke executive privilege, to protect the confidentiality of presidential discussions.
President Donald Trump speaks in the East Room at the White House in Washington, Monday, June 5, 2017.
He reportedly has met with Comey to discuss the probe, and Comey reportedly sought his approval to testify before lawmakers.
The investigation into ties between the Trump campaign and Russian officials is also scaring off people who had been on the fence about joining the administration.
U.S. intelligence officials have said Russian Federation tried to interfere in the election to sway the vote in Trump's favour, a charge the Kremlin has repeatedly denied.
The online news outlet said the NSA report depicted a hacking operation tied closely to Moscow's GRU intelligence directorate that targeted private U.S. companies providing voter registration services and equipment to local governments around the country.