Democrats have kept up their attacks on FBI Director James Comey, accusing him of a double standard after he revealed his agency's probe into more material that might relate to presidential candidate Hillary Clinton's use of a private email server.
Little is publicly known yet about the trove of emails being investigated, other than that they were found during an unrelated probe into the estranged husband of a top Clinton aide.
Comey himself said in a brief letter about the issue to members of Congress on Friday that "we don't know the significance of this newly discovered collection of emails".
But Clinton's Republican rival, Donald Trump, seized on the news of the probe to press his longstanding charge that Clinton lacks integrity, hoping he can make an improbable late comeback and win the election.
Opinion polls have shown Clinton's lead over Trump was narrowing slightly since early last week.
It is not yet known if the email controversy will hurt her support. Millions of Americans have already cast their ballot in early voting.
The FBI spent a year investigating Clinton's use of a private email server, instead of government systems, while she was secretary of state from 2009 to 2013.
Comey concluded in July that while Clinton and her staff had been "extremely careless" in handling classified information there were no grounds for any charges.
The Clinton campaign and its supporters furiously attacked Comey for releasing new information that raised questions but provided no details so close to election day.
Some party leaders said the agency was concealing damaging information about the Trump campaign.
The White House steered clear on Monday of direct criticism of Comey, who was appointed by Democratic President Barack Obama in 2013.
Clinton was campaigning in Ohio on Monday and trying to move beyond the controversy, telling supporters to keep focused on winning the election.
"There is no case here," she said at a rally at Kent State University. Earlier, she told a restaurant patron at a cafe in Cleveland that the email affair is, "Lots of noise. Lots of distractions. Throwing stuff at me. And we've just got to keep people up, moving and voting."
Democratic Representative Elijah Cummings hammered this accusation on Monday, urging the FBI to release information on Trump and his advisers' dealings with Russia.
An FBI spokeswoman said late on Sunday: "When we receive the letter it will be handled through our usual process in responding to members of Congress," referring to Reid's accusation.
