WASHINGTON — The F.B.I. director, James B. Comey, on Tuesday recommended no criminal charges against Hillary Clinton for her handling of classified information while she was secretary of state, lifting an enormous legal cloud from her presidential campaign less than two hours before she boarded Air Force One for her first joint campaign appearance with President Obama.
But on a day of political high drama in Washington, Mr. Comey rebuked Mrs. Clinton as being “extremely careless” in using a private email address and server. He raised questions about her judgment, contradicted statements she has made about her email practices, said it was possible that hostile foreign governments had gained access to her account, and declared that a person still employed by the government — Mrs. Clinton left the State Department in 2013 — could have faced disciplinary action for doing what she did.
To warrant a criminal charge, Mr. Comey said, there had to be evidence that Mrs. Clinton intentionally transmitted or willfully mishandled classified information. The F.B.I. found neither, and as a result, he said, “our judgment is that no reasonable prosecutor would bring such a case.”
The Justice Department is highly likely to accept the F.B.I.’s guidance, which a law enforcement official said also cleared three top aides of Mrs. Clinton who were implicated in the case: Jake Sullivan, Huma Abedin and Cheryl D. Mills. Attorney General Loretta Lynch said last week that she would accept the recommendation of the F.B.I. and career prosecutors in the case after a storm of criticism about an impromptu meeting between her and former President Bill Clinton on an airport tarmac in Phoenix.
Mr. Comey’s 15-minute announcement, delivered with no advance warning only three days after his investigators interviewed Mrs. Clinton in the case, riveted official Washington and is likely to reverberate for the rest of the campaign. In offices across the capital, all eyes turned to television screens to hear the outcome of a yearlong investigation that could have thrown the 2016 presidential election into disarray and changed history.
As Mr. Comey strode to the lectern at the F.B.I. headquarters at 11 a.m., Mrs. Clinton was waiting backstage a few blocks away to address the National Education Association. Her aides said she did not know what Mr. Comey was going to say. Five minutes into Mr. Comey’s remarks, and before he announced that the F.B.I. would not seek charges, a smiling Mrs. Clinton began her speech.
By 2:45 p.m., she and Mr. Obama were descending the stairs of Air Force One for a campaign rally in Charlotte, N.C., while back in Washington the State Department spokesman, John Kirby, was fending off questions from reporters about what Mr. Comey described as the department’s lax security in handling classified information.
White House officials said Mr. Obama also did not know about Mr. Comey’s plans ahead of time. The F.B.I. director said he did not coordinate the statement with the Justice Department or any other agency. “They do not know what I am about to say,” he declared.
A Republican former federal prosecutor, Mr. Comey seemed at first to be laying the groundwork for some kind of legal charge. Speaking sternly, and in far more detail than he usually does, he listed several previously undisclosed findings from the F.B.I.’s investigation:
■ Of 30,000 emails Mrs. Clinton handed over to the State Department, 110 contained information that was classified at the time she sent or received them. Of those, Mr. Comey said, “a very small number” bore markings that identified them as classified. This finding is at odds with Mrs. Clinton’s repeated assertions that none of the emails were classified at the time she sent or received them. The F.B.I. did not disclose the topics of the classified emails, but a number of the 110 are believed to have involved drone strikes.
■ The F.B.I. discovered “several thousand” work-related emails that were not in the original trove of 30,000 turned over by Mrs. Clinton to the State Department. Three of those contained information that agencies have concluded was classified, though Mr. Comey said he did not believe Mrs. Clinton deliberately deleted or withheld them from investigators.
■ In saying that it was “possible” that hostile foreign governments had gained access to Mrs. Clinton’s personal account, Mr. Comey noted that she used her mobile device extensively while traveling outside the United States, including trips “in the territory of sophisticated adversaries.”
■ Mrs. Clinton used multiple private servers for her personal and government business, not just a single server at her home in New York that has been the focus of media reporting for more than a year. Her use of these servers — some of which were taken out of service and stored — made the F.B.I.’s job enormously complicated as it struggled to put together, in Mr. Comey’s words, a jigsaw puzzle with “millions of email fragments” in it.
Despite all that, Mr. Comey said the F.B.I. did not find that Mrs. Clinton’s conduct revealed “intentional misconduct or indications of disloyalty to the United States or efforts to obstruct justice.” But a person in her position, he said, “should have known that an unclassified system was no place” for the emails she was sending. And he said it raised troubling questions about how the State Department handled classified information.
The White House press secretary, Josh Earnest, declined to comment, except to say it was clear from Mr. Comey’s remarks that “they’ve looked at this in excruciating detail.” Mr. Obama, he said, remained “enthusiastic” about Mrs. Clinton’s candidacy.
The Clinton campaign clearly hoped that the announcement would bring to a close a saga that has haunted Mrs. Clinton since March 2015, when the existence of her personal email account surfaced.
“We are pleased that the career officials handling this case have determined that no further action by the department is appropriate,” said the campaign’s spokesman, Brian Fallon. “As the secretary has long said, it was a mistake to use her personal email and she would not do it again. We are glad that this matter is now resolved.”
Republicans seized on Mr. Comey’s sharp criticism, saying it raised doubts about Mrs. Clinton’s fitness for high office. Donald J. Trump, the presumptive Republican nominee, asserted in a post on Twitter that David H. Petraeus, the former C.I.A. director, had been charged for doing far less than Mrs. Clinton, and the lack of charges showed that the system was “rigged.”
In fact, F.B.I. officials have long said that what Mr. Petraeus did — knowingly handing a diary with classified information to his biographer and lover, then lying about it to investigators — was worse than what Mrs. Clinton did. In the Petraeus case, the F.B.I. recommended a felony indictment, but the Justice Department allowed him to plead to a misdemeanor. The deal that Mr. Petraeus received shadowed Mrs. Clinton’s case from the start because it appeared to set a higher bar for bringing charges against her.
“In looking back at our investigations into the mishandling or removal of classified information,” Mr. Comey said, “we cannot find a case that would support bringing criminal charges on these facts.”
Congressional Republicans swiftly called for the F.B.I. to release more details about its findings. “If it wants to avoid giving the impression that the F.B.I. was pulling punches,” said Senator Charles E. Grassley, the Republican chairman of the Senate Judiciary Committee, “the agency must now be more transparent than ever in releasing information.”
Speaker Paul D. Ryan was equally critical. “While I respect the professionals at the F.B.I., this announcement defies explanation,” he said in a Twitter post. “No one should be above the law.”
For an agency that seemed to be in no rush, the F.B.I.’s investigation wrapped up quickly. By the time the investigators interviewed Mrs. Clinton in three and a half hours of questioning on Saturday, they had compiled months of findings. Mrs. Clinton appeared to say nothing to contradict what they had already discovered about how the private server was used, a law enforcement official said. The investigators then worked with Mr. Comey through the holiday weekend to review her testimony and determine whether there was any new information that might warrant criminal charges, law enforcement officials said. They found none.
For weeks, F.B.I. agents expected the investigation would not yield charges. They shared Mr. Comey’s conclusion that Mrs. Clinton had showed poor judgment but that she had not committed a crime.
In the spring, Mr. Comey declared that the campaign calendar would not dictate the pace of the investigation. But the Democratic National Convention begins on July 25 in Philadelphia, and F.B.I. officials did not want to be seen as influencing the outcome of the election after the nomination.
Mr. Comey’s announcement was believed to be the first time that the F.B.I. had ever publicly disclosed its recommendations to the Justice Department about whether to charge someone in any high-profile case, let alone a presidential candidate. His decision to announce the results of the investigation was made before the uproar over Ms. Lynch’s meeting with Mr. Clinton, according to a law enforcement official. He decided to make his findings public, the official said, because he wanted to make the F.B.I.’s position clear before referring the case to the Justice Department.
While the F.B.I.’s recommendation spares Mrs. Clinton and her aides criminal charges, it does not remove the possibility that they could be denied security clearances if Mrs. Clinton is elected and she appoints them to jobs that require such clearance. The State Department plans to conduct its own administrative review after the Justice Department acts.
“We don’t share the broad assessment made of our institution that there’s a lax culture here when it comes to protecting classified information,” said the State Department spokesman, John Kirby. “We take it very, very seriously.”