The FBI has reportedly obtained a warrant to search thousands of emails beloning to top Hillary Clinton aide Huma Abedin.
Ms Abedin's emails are believed to have been found on the laptop of her estranged husband Anthony Weiner.
The discovery prompted FBI Director James Comey to write to members of Congress informing them of a new inquiry related to Hillary Clinton's emails.
Harry Horton reports from Washington.
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There's been no time for the dust to settle following FBI Director James Comey's shock announcement on Friday.
Hillary Clinton's team face a difficult week with the prospect of a daily trickle of details about the FBI's new inquiry into emails possibly linked to the Democratic nominee.
Her campaign team have turned their fire onto James Comey. Clinton Press Secretary Brian Fallon released a video placing questions firmly at the FBI's front door.
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And later on Sunday, the Democratic leader in the US Senate - outgoing Senator Harry Reid - accused James Comey of breaking the law. In a letter, he said Mr Comey may have violated the Hatch Act, which bars officials from using their position to influence an election.
For the Trump campaign - Comey's actions are a gift. Hillary Clinton's emails are now the main focus of Donald Trump's rallies.
Speaking to supporters in Colorado on Sunday, Donald Trump accused Hillary Clinton of playing the victim card.
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The opinion polls were narrowing for several days before news of the new FBI probe came out. It will take some time before they fully reflect any change on voters minds.
And with reports that the FBI have more than 650,000 emails to search through, it's unlikely the inquiry will conclude before the election in 8 days time.
What is certain is that Donald Trump's campaign are far more confident about winning this election than they were a week ago.
But picture this - the choice in voters minds now is to back a man accused of sexual assault, or vote for a woman who might be under some sort of criminal investigation by the FBI.
For many Americans - they just can't wait for this unpredictable and unprecedented election to be over.
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