Officials speaking with reporters on the condition of anonymity is common, and several did so for this report. But the level of specificity that has emerged in recent days about a politically sensitive investigation on the eve of an election is unusual — a sign of the deep tensions inside the Justice Department.

A spokeswoman for the FBI’s New York field office and spokesmen for the Justice Department and FBI headquarters declined to comment for this report. FBI Agents Association President Thomas F. O’Connor said in a statement: “Agents undertake all investigations with an unwavering focus on complying with the law and the Constitution, and perform their mission with integrity and professionalism. Any implication that Agents are unwilling or incapable of performing effective investigations — or implications that Agents do not respect the confidentiality of those investigations — is simply false.”

If Clinton is elected, Comey might have to contend with one or more investigations involving a sitting president. If she is not, he might face criticism for upending her bid.

Anderson, the former FBI official, said Comey will have to work quickly to finish the restarted email review, then talk to leaders and visit field offices to ease the tensions in the bureau and help mend public perceptions of the FBI. Comey has repeatedly said in the past that is important to him.