Days before he was fired, U.S. FBI director James Comey asked for more money and personnel to support an intensifying probe into possible collusion between advisers to Donald Trump and the Kremlin.
The request, first reported by The New York Times, adds to the tensions surrounding Mr. Trump's sudden dismissal of the country's top law-enforcement official on Tuesday and raises questions about the future course of a highly sensitive investigation.
While Mr. Trump has the authority to remove the head of the Federal Bureau of Investigation, no president has exercised that power at a time when the FBI is engaged in an probe that targets the White House. By removing Mr. Comey, Mr. Trump has opened himself up to charges that he is seeking to impede the inquiry.
On Wednesday, Democrats renewed their demands for the appointment of an independent special prosecutor to handle the Russia investigation. Some Republicans expressed concerns about the manner and timing of Mr. Comey's dismissal, but they stopped short of calling for a special prosecutor.
Mr. Trump lashed out on Twitter, calling Democrats "phony hypocrites" who were pretending "to be aggrieved" by Mr. Comey's firing. He defended his decision to oust Mr. Comey, telling reporters at the Oval Office that Mr. Comey "wasn't doing a good job."
The President's stated rationale for firing Mr. Comey was that the FBI director had erred by making public – and controversial – statements over the course of the bureau's probe of Democrat Hillary Clinton's private e-mail server.
But according to several media reports, Mr. Trump had grown increasingly incensed by Mr. Comey and the continuing prominence of the Russia probe and resolved to remove him.
On Wednesday morning, Mr. Trump met at the White House with Russian Foreign Minister Sergey Lavrov and Sergey Kislyak, the Russian ambassador to the United States. Mr. Kislyak played a key role in the controversy that led to the firing of Michael Flynn, Mr. Trump's first national-security adviser.
The investigation into the potential ties between Mr. Trump's campaign and Russia began in the summer of 2016 and experts said it would be common for such a complex probe to take a year or more. On Tuesday, CNN reported that federal prosecutors in Virginia had obtained subpoenas for financial records of Mr. Flynn's associates in connection with the investigation.
In a high-profile case such as the Russia investigation, Mr. Comey would have received daily updates on its progress and been involved in all the key decisions, said Dennis Lormel, a 28-year veteran of the FBI who formerly headed its financial-crimes section.
"The people who are running the case are still running the case," Mr. Lormel said. "I don't question the integrity of the agents. I question the impediments they may face."
That sentiment was echoed by a former federal prosecutor who knows Mr. Comey and called his firing "outrageous." The Justice Department, led by Mr. Trump's close ally Jeff Sessions, together with a new FBI director selected by Mr. Trump, could find subtle ways to "slowly strangle" the Russia inquiry by withholding resources or approvals, the former prosecutor said.
Replacing Mr. Comey – a leader with a deeply independent streak who inspired fierce loyalty at the FBI – will be a tall order. Among those reportedly up for consideration to succeed Mr. Comey are Andrew McCabe, the acting director of the FBI; Ray Kelly, the former commissioner of the New York Police Department; John Pistole, a former deputy director of the FBI; and Chris Christie, the governor of New Jersey and an adviser to Mr. Trump's campaign.
"The main message that will come across to those considering the job is, 'Be careful how you handle the White House and people close to the President,'" said Sanford Ungar, a scholar at Georgetown University who wrote a book about the FBI. Mr. Comey was fired four years into what was supposed to be a 10-year term.
Both the Senate and House of Representatives are investigating Russian interference in the election – sifting through documents and questioning witnesses, sometimes publicly and sometimes behind closed doors – and are expected to ultimately issue reports on their findings.
On Wednesday, the Senate Intelligence Committee issued a subpoena ordering Mr. Flynn, the former national-security adviser, to turn over all records related to his contacts with Russia. The move marked a newly forceful turn in the congressional probe.
If it chooses, Congress can ratchet up the pressure on Mr. Trump. For instance, lawmakers could allocate further resources to its current investigations; stall the President's agenda until he agrees to an independent commission, similar to the one that probed the 9/11 attacks; or pass a law appointing a special prosecutor.
Any such moves, however, would require the Republicans, who hold a majority in both chambers, to join with the Democrats. For the most part, the GOP lined up behind Mr. Trump, although some cracks appeared in the unified front.
Richard Burr, the Republican chair of the Senate intelligence committee, said he was "troubled by the timing and the reasoning" of Mr. Comey's firing. "I have found Director Comey to be a public servant of the highest order," Mr. Burr said in a statement. His dismissal "is a loss for the Bureau and the nation."
Chris Edelson, an expert on the presidency and national security at American University in Washington, said it is up to Congress to keep Mr. Trump in check. "This is a President with authoritarian tendencies who does not believe the rules apply to him," Prof. Edelson said. While the GOP has largely stood with Mr. Trump so far, that could change if they feel more pressure from voters.
In the post-Watergate era, presidents have steered clear of doing anything that might be construed as open interference with the FBI's work, despite their frustrations with the investigations it conducted, said Andrew Rudalevige, a political scientist at Bowdoin College who studies the U.S. presidency.
Mr. Trump's decision to fire Mr. Comey is "a bad political call," he added. The use of raw presidential power often masks weakness, Prof. Rudalevige said, since it means that presidents "haven't been able to get what they want through less public and dramatic means."