Comey essentially cleared Clinton just two days before an American presidential election that is much closer than it was before Oct. 28, when, in an equally short, cryptic letter to lawmakers, Comey said the agency had found the e-mails, which were contained on a laptop belonging to Clinton aide Huma Abedin and her estranged husband, Anthony Weiner.

WASHINGTON — An October surprise morphed into a November thunderbolt Sunday, as FBI Director James Comey announced that agents had completed a hasty review of newly discovered e-mails related to Hillary Clinton and concluded, as they had four months ago, that Clinton should not face criminal charges for her suspect handling of classified information on a private server.


If Clinton loses Tuesday, many of her supporters will blame the FBI for creating an environment of suspicion that proved to be unwarranted and helping Donald Trump capture the White House. If she fends off Trump’s late surge and wins, the size of her victory will almost certainly have been diminished by the cloud that hung over her campaign over the last nine days as millions of voters cast early ballots across the country.

Either way, Comey faces deep skepticism from members of both political parties who are baffled that Comey would open the FBI to accusations that it was meddling in a presidential election.

In his letter to key members of Congress Sunday afternoon, Comey said investigators had worked “around the clock” and reviewed all e-mails sent or received from Clinton that were contained on the laptop, which had been found during an investigation of sexually suggestive text messages Weiner allegedly exchanged with a teenager.

“Based on our review, we have not changed our conclusions that we expressed in July,” he wrote. Comey in July criticized Clinton’s e-mail practices, calling them “extremely careless,” but said that they were not criminal and she should not be prosecuted.


Comey revealed very little about the nature of the e-mails, how many there were, or what was found in the review. NBC News reported that nearly all of the e-mails were duplicates of those they had already uncovered in an investigation of Clinton’s use of a private server while she was secretary of state, a probe that began in 2015; others were personal in nature, according to NBC.

Comey on Oct. 28 said the new e-mails “appear to be pertinent to the investigation,” although it did not appear any significant review had taken place. After obtaining a search warrant a few days later, FBI agents began digging through the e-mails.

Comey’s surprise October disclosure had an immediate effect on the presidential campaign and gave Trump’s forces — whose campaign mantra for months has been “Lock Her Up!” — cause for celebration. Clinton’s double-digit national lead nearly evaporated; polls in key battlegrounds tightened. Democrats’ chances of capturing Senate control also dimmed.

As the threat of a renewed investigation lifted, it remained unclear how the news would affect the final two days of the race.

“We were always confident nothing would cause the July decision to be revisited,” said Brian Fallon, the Clinton campaign press secretary. “Now Director Comey has confirmed it.”

During a rally in Cleveland, where she was accompanied by NBA superstar LeBron James, Clinton never mentioned the Comey letter, choosing instead to focus on Trump.

“His vision of America is so dark and divisive. It’s not the America I see,” she said. “We’ve arrived at a reckoning. Our core values are being tested.”


Watch: Clinton in N.H.

Campaigning in Michigan, Trump said Clinton benefited from a “rigged’’ system and questioned the FBI’s ability to conduct its review so quickly.

“You can’t review 650,000 new e-mails in eight days. You can’t do it, folks,” Trump said, adding, “Hillary Clinton is guilty. She knows it, the FBI knows it, the people know it, and now it’s up to the American people to deliver justice at the ballot box on November 8.”

Other top Trump supporters questioned the veracity of Comey’s new conclusions.

“Comey must be under enormous political pressure to cave like this and announce something he can’t possibly know,” Newt Gingrich wrote on Twitter.

Trump’s campaign manager, Kellyanne Conway, questioned whether FBI agents could have gone through so many e-mails within a week.

“He’s mishandled this investigation from the beginning, and this proved it yet again,” she said on MSNBC.

Donald Trump appeared Sunday at a rally in Sioux City, Iowa. Carlo Allegri/Reuters

Some Democrats were enraged, calling on the Justice Department to develop new procedures to prevent something similar from happening in the future. President Obama last week criticized Comey from deviating from guidelines of not interfering so close to an election, saying, “We don’t operate on incomplete information. We don’t operate on leaks. We operate based on concrete decisions that are made.”

“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 Senator Dianne Feinstein, a California Democrat and ranking member of the Senate Intelligence Committee. “Today’s letter makes Director Comey’s actions nine days ago even more troubling. There’s no doubt that it created a false impression about the nature of the agency’s inquiry.”


House Speaker Paul Ryan, who has had a shaky relationship with Trump, put out a statement discounting the latest development:

“Regardless of this decision, the undisputed finding of the FBI’s investigation is that Secretary Clinton put our nation’s secrets at risk and in doing so compromised our national security. Fortunately, the American people have the opportunity to ensure Secretary Clinton never gets her hands on classified information again.”

As the news jolted the campaign on Sunday, Clinton and Trump were sprinting toward the home stretch, delivering closing speeches and packing their schedules with last-minute stops in battleground states that will decide the election on Tuesday.

With polling showing razor-thin margins in several key states — including New Hampshire — both campaigns have cause for optimism. For Clinton, it’s that she is ahead in most of the states, and has numerous paths to the presidency while Trump needs to play a perfect game.

For Trump, it’s that he has been the one with momentum in the final days — largely thanks to Comey’s earlier disclosure — closing the gaps in even traditionally Democratic states that weren’t in play until recently, such as Michigan.

Watch: Trump in Mich.

“It’s also, I think, a little bit of a surprise to everyone involved that Donald Trump is closing and he’s got the momentum going into Tuesday,” Reince Priebus, the chairman of the Republican National Committee, said on CBS News’ “Face the Nation” several hours before Comey’s announcement.


Watch: Priebus on ‘Face the Nation’

In the final days, Michigan has suddenly become a point of focus for both campaigns. It is a striking turnabout that could be troubling for Democrats who are now focusing on a reliably blue state in the last stretch.

Bill Clinton visited on Sunday, and Hillary Clinton and President Obama planned to make stops on Monday.

Clinton’s campaign suggested that the visits were added more out of caution than any sense of worry. Clinton has never trailed in a Michigan poll during this campaign.

“We feel like we got a lead in Michigan,” John Podesta, the Clinton campaign chairman, said on NBC’s “Meet the Press.” “We want to hold onto it and we think we can do that.”

While Clinton still appears to have an edge, the race has clearly become far more competitive than it once was, with Trump nipping at Clinton’s heels in key states.

An NBC/Wall Street Journal poll released on Sunday showed Clinton with a four-point national lead, down from 11 points more than three weeks earlier, before Comey’s initial bombshell. A CBS News poll had Clinton and Trump essentially tied in Florida and Ohio. In Iowa, a Des Moines Register poll had Trump with a 7-point lead.

Trump is eager to flip several reliably Democratic states, but his itinerary has been so scattered that it is not clear which ones he thinks he can win.

On Sunday, he traveled from Iowa to Minnesota to Michigan to Pennsylvania to Virginia. Aside from Iowa, he trails in the recent polls conducted in the other four states.

“It looks like he’s just trying to go everywhere all at once,” Clinton campaign manager Robby Mook told reporters on Saturday afternoon. “As far as I’m concerned, the more time he spends in Minnesota and Nevada the better. We have tried to calibrate our schedule to be in states at the peak time for voting.”

Clinton campaigned in Cleveland before appearing with James Taylor and Khizr Khan in Manchester, N.H.

“We have to get out and make sure we vote,” LeBron James said in Cleveland. “This woman right here has the brightest future for our world.”

Watch: James, Clinton in Cleveland

Clinton on Monday plans to campaign in Pittsburgh; Grand Rapids, Mich.; Philadelphia; and then Raleigh, N.C. Trump is planning to be in Sarasota, Fla.; Raleigh; and Scranton, Pa., before a closing rally in Manchester, N.H.

The 2016 election

Matt Viser can be reached at matt.viser@globe.com. Follow him on Twitter @mviser.