There is a "general fear that the White House will try to interfere with the investigation" into Russian election meddling, one FBI source said. "The first target will be the leak investigation, and then, long term, if Donald Trump appoints some crony, that could make the whole Russia investigation go away."
Acting FBI Director Andrew McCabe told senators Thursday, "I strongly believe that the Russian investigation is adequately resourced."
One source said Deputy Attorney General Rod Rosenstein isn't inclined to make a change unless the FBI investigation appears to be imperiled, and at this point, FBI officials are confident that the investigation is moving ahead, despite Comey's abrupt firing. The investigation is overseen by Dana Boente, the US attorney in Alexandria, Va., who now also serves as the head of national security prosecutions at Justice Department headquarters.
Meanwhile, current and former agents said the startling way that Comey was fired -- he learned the news from television reports while on a trip to Los Angeles -- infuriated and unified many agents regardless of how they felt about the former FBI director personally.
A federal law enforcement source familiar with morale in the FBI's Los Angeles field office -- where Comey was when he saw the TV reports that he had been fired -- said "it varies from sadness to ... bewilderment, maybe."
One longtime FBI supervisor tells CNN: "Everyone is disappointed at what happened, and we feel we lost a great director. I was appalled by Sarah Huckabee Sanders saying that several agents called her saying that they were happy he was gone. I don't know a single one."
One street agent also praised Comey to CNN, saying, "Director Comey recognized that street agents were the backbone of the FBI."
Opinion is divided within the bureau over the job that Comey did during his three-year tenure, with views split along political lines over the bureau's unusually prominent role in the fall presidential campaign, one former senior agent said. Some agents who dislike Hillary Clinton believe Comey went too easy on her by not recommending criminal charges, while others think he helped Trump win the election by injecting the FBI so deeply into the race.
One law enforcement source said Comey's actions were sometimes the subject of debate among agents, but most respected him as a leader and believed that "his decisions were made with good intentions."
One veteran FBI supervisor said that although he found Comey to be well-liked and respected by most agents, there was also growing concern that his actions, "right or wrong," resulted in an unwanted focus on the FBI in recent months.
"The bureau does not like to be in the limelight," said the agent, who asked not to be named. "It was handled like if he'd stayed another minute, it would have caused further damage to the bureau, like there was a national security concern. It's just insulting, we thought."
But there is a clear consensus and outrage over the White House's decision to send the President's bodyguard to deliver the termination letter to the FBI while Comey himself was at a field office in Los Angeles, he said.
"It was classless," said the former agent, who maintains close ties to many agents. "He deserved more respect than that."
"Most people in the bureau have not experienced something like this," one source said. "It feels like [the FBI] is going to be rudderless for a while. That's an uncomfortable feeling."
Amid the turmoil, many of the bureau's 13,000 agents are simply trying to keep their heads down and move past this week's events with hopes of getting a new director in place as quickly as possible.
"Our guys are professionals," said Paul Nathanson, a spokesman for the FBI Agents Association. "They were working their cases last week, they're working their cases this week, and they'll be working their cases next week. What choice do they have?"
The association has already made known its choice for a new director: Mike Rogers, the former agent and Michigan Republican congressman.
Even as many agents bemoan the firing of Comey and the way he was treated, "they're turning the page," Nathanson said.