Issue's reappearance has potential of fatally hurting Clinton's campaign
If you asked any pundit last Thursday who they thought would win the presidential election in two weeks, nearly all would have said Mrs Hillary Clinton.
On Friday, after a bombshell announcement from the Federal Bureau of Investigation (FBI) that it was restarting its investigation into her use of a private e-mail server, all that changed.
"If you asked me this three hours ago, anything can still happen but it all looks very good for Secretary Clinton," said Dr Barbara Perry, director of presidential studies at the University of Virginia's Miller Centre. "Now, the 'anything can still happen' situation might just have happened."
While the extent of the fallout is yet to be fully known, most agree that this revelation - more so than any of the previous iterations of the long-running e-mail scandal - has the potential to inflict real harm on her campaign.
For one thing, the announcement from the FBI director - while vague and non-committal - contains a very serious allegation.
While the new e-mail discovered could amount to nothing, it could also amount to a criminal charge.
Said University of North Carolina Charlotte political science professor Eric Heberlig: "The last thing you want is the words 'FBI' and 'investigation' to be associated with your organisation heading into an election. The FBI story has the real potential to change the dynamics of the race. Right now the statement they put out is just so vague the Clinton campaign can't respond to it effectively and everyone is just going to assume the worst."
And in all likelihood, those uncertainties will not be cleared up by election day on Nov 8.
How big a swing this causes in the polls remains to be seen and depends a lot on how voters react to it.
In the Clinton campaign's nightmare scenario, the revelations peel off the independents and moderate Republicans she had attracted while suppressing the turnout among the progressive supporters of Senator Bernie Sanders that were never really comfortable with her.
CLINTON'S E-MAIL SAGA
Here's a closer look at the FBI's investigation into Hillary Clinton's e-mail:
30,000 initially turned over by Mrs Clinton's lawyers, deemed work-related, returned to the State Department in December 2014.
• Eight chains included "top secret" information
• 36 chains included "secret" information
• Eight chains included "confidential" information, the lowest level of classification
• 2,000 e-mail have since been classified "confidential"
• FBI director James Comey said a very small number of e-mail had classified markings when they were sent.
14,900 additional work-related e-mail that Mrs Clinton did not turn over to the State Department which were uncovered by the FBI during the course of its investigation.
• More than 9,000 e-mail were personal and will not be released.
• About 5,600 will be released, many not until well after Election Day. At least 75 have been released so far.
Unknown number of additional e-mail that may be pertinent, according to the FBI last Friday. These were found after the bureau seized at least one electronic device once shared by Anthony Weiner and his estranged wife Huma Abedin, an aide to Mrs Clinton.
• The number of e-mail are in the thousands, according to law enforcement officials.
The best-case scenario is that the revelation from the FBI turns out to be a damp squib, either because of another Trump scandal or simply because it doesn't change any attitudes about Mrs Clinton.
Mrs Clinton already had a problem convincing voters she was trustworthy. And it is possible those concerns are already baked into her current polling advantage.
As Dr Perry put it: "Given the very problematic nature of Donald Trump as a candidate, one argument has been why was the gap between them below 10 points? Why isn't it 15 or more? It could be that the perceptions about her have already made a difference."
Also working in Mrs Clinton's favour is the fact that millions of votes have already been cast in early voting and her lead in the polls - an average of between five and six percentage points - is big enough to give her some room for error.
Then there is the question of whether her opponent can properly maximise the opportunity.
Dr Melissa K. Miller from Bowling Green State University in the key swing state of Ohio said the Trump campaign needs to start investing more in campaign advertising to take advantage of Mrs Clinton's travails.
She added: "Trump needs to exercise the kind of message discipline that has largely eluded him thus far. The bottom line is that the polls and electoral college map still favour Clinton. Even with the recent FBI announcement, Trump has quite a number of disadvantages to overcome in order to win the White House."
A version of this article appeared in the print edition of The Sunday Times on October 30, 2016, with the headline 'New e-mail probe could change everything... or nothing'. Print Edition | Subscribe
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