A new shock hit Hillary Clinton's presidential campaign as the FBI said it is looking into whether there was classified information on a device belonging to the estranged husband of one of her closest aides.
Adding to the drama of the stunning revelation, the FBI uncovered the emails during a sexting investigation of Anthony Weiner, the disgraced ex-congressman who is separated from long-time Clinton aide Huma Abedin.
The Democrat said late she was confident whatever the FBI may find would not change its conclusion from earlier this year - that her use of a private email system as secretary of state did not merit prosecution.
"We don't know the facts, which is why we are calling on the FBI to release all the information that it has," she said.
"Even (FBI) Director (James) Comey noted that this new information might not be significant, so let's get it out."
The news arrived with Mrs Clinton holding a solid advantage in the presidential race. Early voting has been under way for weeks, and she has a steady lead in preference polls.
But the development all but ensures that, even should she win the White House, the Democrat and several of her closest aides would celebrate victory under a cloud of investigation.
It was a day that thrilled Republicans eager to change the trajectory of the race, none more so than party nominee Donald Trump.
"Hillary Clinton's corruption is on a scale we have never seen before," he said while campaigning in battleground New Hampshire.
"We must not let her take her criminal scheme into the Oval Office."
Democrats, still confident Mrs Clinton will prevail in 11 days, were enraged by Mr Comey's decision to disclose the existence of the fresh investigation in a vaguely worded letter to several congressional leaders.
"The FBI has a history of extreme caution near Election Day so as not to influence the results," said California Senator Dianne Feinstein. "Today's break from that tradition is appalling."
It was not until hours after Mr Comey's letter emerged that word came that the source of the new emails was Mr Weiner, the former congressman under investigation for sending sexually explicit text messages to a teenage girl.
"We don't know what to believe," Mrs Clinton said, adding: "Right now, your guess is as good as mine, and I don't think that's good enough."
The development also reignited persistent worries among Democrats that electing the former first lady will restart a cycle of scandal and investigation that could rival the final portion of her husband's term in office.
Congressional Republicans have already promised years of investigations into Mrs Clinton's private email system, and that is only one of the email-related controversies facing her.
The tens of thousands of confidential emails from Clinton campaign insiders that were hacked - she and the government say by Russia - and then released by WikiLeaks have provided a steady stream of questions about her policy positions, personnel choices and ties with her husband's sprawling charitable network and post-presidential pursuits.
In his letter to congressional leaders, Mr Comey wrote that new emails have emerged, prompting the agency to "take appropriate investigative steps" to review information that may be pertinent to its previously closed investigation into Mrs Clinton's private email system.
The FBI ended that investigation in July without filing charges, although Mr Comey said then that Mrs Clinton and her aides had been "extremely careless" in using the system for communications about government business.
Mr Trump accused Mrs Clinton of trying to "politicise" the FBI's decision to investigate the emails.
Speaking at a rally in Cedar Rapids, Iowa, he said Mrs Clinton lied by claiming that Mr Comey only notified Congressional Republicans about the development. Some Democrats were also notified.
Mr Trump went on to say: "The FBI would never have reopened this case unless it was a most egregious offence."
Speaking at a Clinton rally in Florida, President Barack Obama also steered clear of the issue. White House spokesman Eric Schultz declined comment beyond reiterating Mr Obama's continuing support for Mrs Clinton.
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