Four months ago, Comey had said the FBI wouldn't recommend criminal charges.

What has changed since then? Where did the FBI get the new evidence from?

The FBI is currently investigating Clinton’s close aide, Huma Abedin’s estranged Husband, Anthony D Weiner. He is under the agency’s radar for sending illicit text messages to a 15-year-old girl. The FBI says that it found some emails pertinent to the closed investigation into Clinton’s private server on the devices seized from Weiner and Abedin.

The FBI director’s letter to Congress is vague. Comey said the FBI "cannot yet assess whether or not this material may be significant".

But this was sufficient to unite Republicans. Even those, who are no fans of Trump, blasted Clinton for her reckless handling of classified material.

Speaker Paul Ryan, the most powerful Republican leader after Trump, called on “the Director of National Intelligence to suspend all classified briefings for Secretary Clinton until this matter is fully resolved".

Clinton held a four-minute press conference in Iowa and said that, "Voting is underway, so the American people deserve to get the full and complete facts immediately.” She demanded that it was “imperative that the bureau explains this issue in question, whatever it is, without any delay."

Trump’s campaign which has been on the defensive since the release of Access Hollywood tape, got a new lease of life. Trump seized on the issue without any delay. "Hillary Clinton's corruption is on a scale we've never seen before," he said addressing a campaign rally in New Hampshire. “We must not let her take her criminal scheme into the Oval Office."

How will this impact the election? No one is sure.

This is what the latest polls have to say (28 October): LA Times/USC show Trump ahead by 2 points. ABC News poll puts Clinton ahead by 4 points. Both are tied if one were to believe Rasmussen. IBD/TIPP says Clinton leads Trump by 3 points.

At this point, it is advantage Clinton. However, the FBI’s October surprise will definitely put her on the defensive. Her credibility will take a hit. Emboldened by Trump’s low poll numbers, Clinton campaign had announced yesterday that she will be campaigning in Arizona, a state Democrats have won only once since the Second World War. Now, she will have to spend the last 10 days of campaign convincing her own base that she can be trusted.

Trump couldn’t have asked for a better gift this close to the election. His chances of becoming the next president of the United States just got trumped up.