For months, the F.B.I. had investigated whether Mrs. Clinton had broken any laws by using a private email server while she was secretary of state. This past summer, Mr. Comey said that Mrs. Clinton had been “extremely careless” by allowing sensitive information to be discussed outside secure government servers, but that the agency had concluded that Mrs. Clinton had not committed a crime. The investigation was closed.
But on Friday, Mr. Comey notified Congress that the agency had discovered emails, possibly relevant to the investigation, that belonged to Mrs. Clinton’s top aide, Huma Abedin. The emails were discovered on the computer of Ms. Abedin’s estranged husband, Anthony D. Weiner, during a separate investigation into allegations that he had exchanged sexually explicit messages with a teenager.