White House tries to regroup, but Trump isn't helping

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.

White House spokeswoman Sarah Huckabee Sanders said the president's power to invoke executive privilege is "well-established".

Comey, who was sacked by Trump in May, is scheduled to testify in a hearing before the Senate on Thursday.

Within days of Comey's firing, his associates said the former Federal Bureau of Investigation chief kept detailed notes of his White House meetings with Trump, including one instance when the president asked him to pledge his loyalty, which Comey declined to do. Trump later denied Comey's description of the meeting.

Trump's agenda has been overshadowed by the ongoing investigations into whether Trump campaign officials or associates colluded with Russian officials to influence the 2016 election, as well as scrutiny over Trump's firing of Comey.

In firing Comey last month, Trump cited performance issues, while critics accused him of trying to close down the Russian Federation probe.

Comey is scheduled to testify before the Senate Select Committee on Intelligence on Thursday. If Comey wants to tell his story, it will be told - one way or another. Comey declined and said he would be honest, the report said.

It is overshadowing other events in Washington, threatening to dampen already flagging momentum for Trump's legislative agenda of rolling back President Barack Obama's healthcare reforms and overhauling the tax code.

Comey's appearance will be carried on live television.

President Donald Trump signs a decision memo and a letter to members of Congress outlining the principles of his plan to privatize the nation's air traffic control system in the East Room at the White House, Monday, June 5, 2017, in Washington.

Experts have said that James Comey's testimony on Thursday has the potential to be something of an quake to the political landscape.

Senators on the Senate Intelligence committee indicated on Monday morning that they didn't believe Trump would invoke executive privilege, noting that they had not been told that he would. The Justice Department later appointed ex-FBI director Robert Mueller as the special counsel.