There are signs that the race for the White House is tightening amid continuing fall-out from the 11th-hour announcement by FBI director James Comey that he was assessing new emails potentially related to the use of a private email server by Hillary Clinton while Secretary of State.

Most notable were two new polls showing that her Republican rival, Donald Trump, may be finding a way back into the contest by becoming newly competitive in Florida, a key state with a large trove of Electoral College votes, without which he would have no plausible path to victory.

Additionally, a new Washington Post/ABC poll showed Ms Clinton leading Mr Trump by a perilously close two points nationally in a four-way race including Green Jill Stein and Libertarian Gary Johnson at 47 per cent versus 45 per cent, which is inside the margin of error. The same poll had Ms Clinton enjoying a huge 12-point lead just six days earlier.

But it is the movement in his favour in Florida that will particularly encourage Camp Trump. A New York Times Upshot/Siena poll released on Sunday had the GOP nominee up four points in Florida in a four-way race, 46 percent to 42 percent. While Ms Clinton has various ways to reach the 270 Electoral College votes necessary to clinch final victory even without Florida, that is almost certainly not the case for Mr Trump. He has to win it.

All the new polls were conducted before Friday when Mr Comey dropped his new emails bomb, the precise impact of which remains uncertain. However, the anxiety it has created in Ms Clinton’s circle is tangible as one after another of her allies called on Mr Comey to clear up the confusion over what the new emails may or may not contain.

Their existence came to light in a brief letter sent by Mr Comey on Friday to leading members of Congress. It was extremely scant on detail, saying nothing beyond the fact that they may be “pertinent” to the investigation into her email server which the FBI formally concluded in July.

While it is now known that the new emails were found in devices shared by Huma Abedin, one of Ms Clinton’s closest aides, and her husband, from whom she is estranged, Anthony Weiner, there has been nothing more from Mr Comey on why they may be of interest. It even appears that many may be duplicates of emails the FBI has already analysed.

"We never thought we were going to say thank you to Anthony Weiner," Mr Trump declared at a rally in Las Vegas on Sunday, virtually taunting the Clinton campaign on the issue. "Corruption is corrosive to the soul of a Democracy, and it must be stopped. We have one ultimate check on Hillary’s corruption, and that is the power of voting. The only way to beat the corruption is to show up and vote by the tens of millions, including millions of people voting for the first time in their entire lives."

Adding to Democrat frustration has been confirmation that before he sent the letter, Mr Comey was strenuously advised to desist by the Justice Department which argued it would violate long-existing groundrules about not doing anything close to an election that could change its course.

US election 2016: the race for the White House in pictures Show all 12 1 /12 US election 2016: the race for the White House in pictures US election 2016: the race for the White House in pictures Republican U.S. presidential nominee Donald Trump shakes hands with Democratic U.S. presidential nominee Hillary Clinton at the conclusion of their first presidential debate at Hofstra University in Hempstead, New York Reuters US election 2016: the race for the White House in pictures President Barack Obama embraces Democratic nominee Hillary Clinton on stage at the party's convention in Philadelphia US election 2016: the race for the White House in pictures Donald Trump's wife Melania delivered a speech at the GOP convention in Cleveland that was later found to have been cribbed in part from Michelle Obama's 2008 convention address AP US election 2016: the race for the White House in pictures Hillary Clinton talks to reporters aboard her new campaign plane on Labour Day, 5 September, her first 'press conference' since 2015 (Getty Images) US election 2016: the race for the White House in pictures Donald Trump held a joint press conference with Mexican leader Enrique Pena Nieto in Mexico City in August, hours before reiterating his harsh immigration plans at a campaign rally in Arizona Reuters US election 2016: the race for the White House in pictures Bernie Sanders officially endorsed Hillary Clinton, saying his progressive vision for ‘a transformed America’ would be ’best served by the defeat of Donald Trump’ Reuters US election 2016: the race for the White House in pictures Khizr and Gazala Khan appeared at the DNC to slam Trump for his stance on Muslim immigration, citing the case of their son Humayun Khan, who was killed in combat while serving as a Captain in the US Army in Iraq US election 2016: the race for the White House in pictures Libertarian candidate Gary Johnson is doing better in polls than any third party candidate since Ross Perot, 20 years ago Nicholas Kamm/AFP/Getty US election 2016: the race for the White House in pictures Green Party candidate Jill Stein (centre) marches with supporters in Colorado AP US election 2016: the race for the White House in pictures Hillary Clinton and Virginia Senator Tim Kaine at a rally in Kaine's home state in July, days before Ms Clinton tapped him to be her running mate Getty US election 2016: the race for the White House in pictures Trump on the campaign trail with his vice presidential pick, Indiana governor Mike Pence AP US election 2016: the race for the White House in pictures Former Ukip leader Nigel Farage appears at a Trump rally in Mississippi in August, where he told the crowd that he 'wouldn't vote for Hillary Clinton if you paid me'.

It seems that Mr Comey may not even have seen the emails in question. In a subsequent email message to FBI employers on Friday, he said, “we don’t know the significance of this newly discovered collection of emails”. Meanwhile, if he does decide to re-open his investigation, any new findings may not emerge until after election day.

“As far as we know now, Director Comey knows nothing about the content of these emails. We don't know whether they're to or from Hillary at all,” Tim Kaine, her running mate, said on Sunday. He added that if Mr Comey “hasn't seen the emails, I mean they need to make that completely plain. Then they should work to see the emails and release the circumstances of those once they have done that analysis.”

Ms Clinton's campaign chairman, John Podesta, said the director’s handling of the matter was “inappropriate”. He also urged Mr Comey to be more transparent because the disclosure came “in the middle of the presidential campaign so close to the voting”.

Late on Saturday, meanwhile, a group of four Democratic senators – Patrick Leahy of Vermont, Dianne Feinstein of California, Thomas Carper of Delaware and Benjamin Cardin of Maryland – wrote to Mr Comey and Attorney General Loretta Lynch demanding a full explanation of the FBI’s actions by Monday at the latest.

“We request you provide us with more detailed information about the investigative steps being taken, the number of emails involved, and what is being done to determine how many of the emails are duplicative of those already reviewed by the FBI,” they wrote.

The first sign of Mr Trump closing the gap with his Democratic rival in the Sunshine State came in the middle of last week, when a Bloomberg News poll gave him his first lead there for several weeks. Sunday also saw the release of an NBC News/Wall Street Journal/Marist poll that had them essentially tied in Florida with Ms Clinton at 45 per cent and Mr Trump at 44 per cent.