White House: Trump thought about firing Comey since Election Day.

Washington (CNN)President Donald Trump had been thinking about firing FBI Director James Comey since Election Day, White House deputy press secretary Sarah Huckabee Sanders said Wednesday.

"The President has lost confidence in Director Comey and, frankly, he'd been considering letting Director Comey go since the day he was elected," Sanders told reporters, adding that Deputy Attorney General Rod Rosenstein had raised concerns about the former FBI chief on Monday, prompting Trump to ask him to put his recommendation in writing.

Behind the scenes of James Comey's epic firing

Revelations that Trump had been unconvinced by Comey for his entire transition and presidency were surprising given the White House had previously expressed confidence in the ousted FBI chief multiple times. Sanders also said Trump was not the only one to lose confidence in the FBI director, adding there were deep reservations about him inside the FBI.

Sanders also said that Trump didn't regret not firing Comey sooner, saying he "wanted to give Director Comey a chance."

She also pointed to a "big catalyst" from last week congressional testimony by the former FBI chief when he related how he held a news conference without notifying his superiors last year. In the blockbuster appearance, Comey announced that Hillary Clinton would not face charges over her email server but also heavily criticized her handling of classified material.

"Director Comey made a pretty startling revelation that he had essentially taken a stick of dynamite and thrown it into the Department of Justice by going around the chain of command," Sanders said.

"That is simply not allowed," she said.

White House: Comey had missteps and mistakes 00:51

Meanwhile, Comey asked the Justice Department for more resources for the agency's investigation into Russian meddling of the US election and ties to Trump's presidential campaign, just the week before the President fired him.

Comey told the heads of the Senate intelligence committee that he went to Deputy Attorney General Rod Rosenstein last week and pushed for more resources to be devoted to the Russia investigation, according to two sources familiar with the discussion.

Justice Department spokesperson Sarah Flores denies Comey asked Rosenstein for more resources. She called reporting to the contrary "100% false," and told reporters she spoke directly with Rosenstein about the reports.

Senate Intelligence Chairman Richard Burr, R-North Carolina, and Democratic Sen. Mark Warner of Virginia met Monday with Comey and urged him to speed up the Russia investigation. Comey acknowledged in this discussion that things were moving slowly.

Warner told CNN Wednesday he has asked Comey to testify before the committee Tuesday. It is an invitation only at this point -- no word yet if he will appear.

Before Rosenstein, Comey had been working with the acting deputy attorney general Dana Boente. Comey's requests for funds was first reported by The New York Times.

In the wake of Comey's firing, a fierce political battle has erupted, as Democrats step up demands for a special prosecutor but Republican leaders hold the line to shield the White House.

With Washington still in disbelief over Tuesday's dramatic events that sent shockwaves across the nation, Trump blasted criticism of his sudden move, declaring that the former FBI chief "wasn't doing a good job."

But the President's comments did little to dispel the controversy over the firing of Comey: the FBI director overseeing the bureau's probe into whether there were any links between Trump campaign aides and Russia at a time when Moscow is accused of meddling in last year's election.

Critics claimed that Trump was trying to shut down the FBI Russia investigation. They ridiculed the White House's rationale for the firing -- that it was over Comey's handling of the Clinton email investigation that many Democrats believe cost the former secretary of state the presidency.