Nine days after throwing the presidential race into turmoil,
The verdict, less than 48 hours before election day, left Democrats still fuming over what party leaders saw as improper political meddling, which caused polls to tighten across the country.
Republicans brushed off Comey's findings and continued to accuse Clinton of poor judgment and negligence in handling classified information.
Comey said agents had worked “around the clock to process and review” emails found on a computer owned by former New York Rep.
"During that process, we have reviewed all of the communications that were to or from Hillary Clinton while she was secretary of State," Comey wrote. "Based on our review, we have not changed our conclusions that we expressed in July with respect to Secretary Clinton."
At that time, the FBI director chided Clinton for being "extremely careless" in setting up a private email server in the basement of her New York home, which allowed her to communicate outside official channels and the security protocol for government emails.
But he said there was no basis for bringing criminal charges.
Of the hundreds of thousands of emails on Weiner's computer, it turned out that only a few thousand were related to Abedin and relevant to the Clinton email probe, a federal law enforcement official said.
Nearly all of those were duplicates of emails the FBI already had read, which the investigators were able to determine fairly quickly by using computer programs that rapidly compare texts.
None of the remaining emails rose to a level that would cause agents to reconsider whether Clinton or her aides had knowingly mishandled classified information, the official said.
Clinton, who spent Sunday hopscotching from Pennsylvania to Ohio to New Hampshire, did not comment publicly on Comey's latest announcement. She stuck to a recitation of policy proposals such as more affordable college and criminal justice reforms.
But campaign officials expressed their satisfaction with the FBI's findings.
"We are glad this matter is resolved," spokeswoman Jennifer Palmieri told reporters en route to a campaign stop in Cleveland, where the Democratic nominee appeared at a get-out-the-vote rally with basketball star LeBron James.
The GOP nominee had lately taken to praising the FBI after questioning the integrity of the agency's initial email probe. He did not specifically mention Sunday's developments before the boisterous crowd at the Minneapolis airport.
Instead, Trump renewed his charges of cronyism in the nation's capital.
"She's protected by a rigged system," he said. "She shouldn't even be allowed to run for president. She is the most corrupt person ever to seek the presidency of the United States."
But later, at a stop in the Detroit suburbs, Trump was more sharply critical of the FBI.
"You can't review 650,000 new emails in eight days," Trump told a rowdy crowd of thousands at an outdoor amphitheater in Sterling Heights.
"You can't do it, folks. Hillary Clinton is guilty. She knows it. The FBI knows it. The people know it," he said. "And now, it's up to the American people to deliver justice at the ballot box on Nov. 8."
Fellow Republicans chimed in, saying the FBI's decision against prosecuting Clinton was hardly an exoneration.
"Secretary Clinton put our nation's secrets at risk and in doing so compromised our national security," House Speaker Paul D. Ryan asserted. "She simply believes she's above the law and always plays by her own rules."
Legalities aside, Comey's announcement — which caught many by surprise — undercut the central political argument that Trump had been making against Clinton in the closing days of the presidential race.
He repeatedly warned that, if elected, Clinton would be crippled by a federal indictment and a tangle of congressional investigations into her email server.
Whatever their relief Sunday, Democrats were still outraged the emails had again become a central issue — especially so close to the election. Many saw Comey's Oct. 28 letter as a violation of Justice Department rules designed to prevent investigative actions from influencing voters.
Even if Clinton wins the White House, Democrats fear the renewed controversy surrounding her emails — which dominated news headlines for more than a week — damaged their prospects in several close Senate races that could determine control of the chamber.
"The October surprise that came only 11 days before election day has unfairly hurt the campaign of one candidate and changed the tenor of this election," said California Democratic Sen. Dianne Feinstein, who suggested Comey's letter Sunday made his actions "even more troubling."
"There's no doubt that it created a false impression about the nature of the agency's inquiry," she said. "I believe the Justice Department needs to take a look at its procedures to prevent similar actions that could influence future elections."
Comey was appointed by President Obama in 2013 to a 10-year term as head of the FBI. He prides himself on his independence and tangled with the White House in his previous job as a senior Justice Department official in the George W. Bush administration.
The fact that Comey is a Republican, however, coupled with a seeming deluge of leaks damaging to Clinton from current or former FBI agents, elevated the anger among Democrats.
Former government officials and outside legal experts with knowledge of the case had said in recent days that the chances were slim that any of the newly found emails would change the FBI's previous conclusions.
During the nearly yearlong investigation of Clinton's email practices, FBI agents had interviewed dozens of witnesses, conducted forensic tests and examined tens of thousands of messages.
Even before Comey's letter, Clinton had reason to look ahead with optimism.
A final round of polling released Sunday affirmed the state of play heading into the campaign's final 48 hours: a solid, if not overwhelming, lead for the Democratic nominee and a struggle for Trump to amass the 270 electoral votes needed to capture the White House.
Early voting figures in Florida, a state Trump must carry, showed an outpouring of Latinos and African Americans, two of the groups strongest in their support for Clinton.
In Ohio, another must-win state for Trump, the two candidates are effective
ly tied. He trails in both Pennsylvania and Michigan, Democratic-leaning states he has aggressively targeted.
Still, as Trump traveled Sunday through several battleground states — Iowa, Minnesota, Michigan, Pennsylvania, Virginia — his camp insisted a history-making upset was in the offing.
"We've been expanding our map, and we are now competing in states where people wrote us off months ago," Kellyanne Conway, Trump's campaign manager, said in a conference call with reporters.
But there was little independent evidence to support that assertion.
Minnesota, for instance, hasn't voted Republican in a presidential election since 1972 — the longest such streak in the country — and Trump has not led a single poll conducted there over the last 15 months.
Barabak reported from San Francisco and Lauter and Wilber from Washington. Times staff writers Michael Finnegan in Minneapolis and Chris Megerian in Cleveland contributed to this report.