Long before the presidential campaign entered its final and most intense phase, political observers had identified two potential "black swan" events that could drastically alter the race: a health scare and a terror attack.
The United States might very well have had both in one week.
Last Sunday, Democratic Party nominee Hillary Clinton was forced to leave a Sept 11 memorial event early and her aides subsequently revealed she had pneumonia.
Two days ago, a blast injured 29 in New York City. Though it was described as an act of terror by New York Governor Andrew Cuomo, he stressed there were currently no links to international terrorism. Still, Republican nominee Donald Trump wasted no time in implying those links.
Speaking about the issue less than an hour after news of the explosion emerged, Mr Trump told a rally in Colorado: "I must tell you that just before I got off the plane, a bomb went off in New York and nobody knows what's going on.
"But boy,we are living in a time - we better get very tough, folks... It's a terrible thing that's going on in our world, in our country and we are going to get tough and smart and vigilant."
His Democratic Party rival Hillary Clinton was more cautious, saying she would speak further "when we actually know the facts".
"I think it's always wiser to wait until you have information before making conclusions," she said.
Their differing responses speak to the political calculations the candidates are making about how the incident is going to affect the race.
For Mr Trump, the belief is that voters want a strong-man response to terror. He has often spoken very bluntly about bombing the Islamic State in Iraq and Syria militant group. He also famously put forward the controversial proposal to temporarily ban all Muslims from entering the US.
Mrs Clinton clearly believes that the better way to appeal to voters concerned about terrorism is to present a steady hand.
Currently, polls offer few clues as to who is making the better argument, although nearly all stress that security and terrorism are among the top issues at the election.
Though surveys from early in the race tended to give an edge to Mr Trump on the question of who is more trusted on the issue of terrorism, that no longer appears to be the case. A Fox News poll released last month found both candidates are essentially tied on the question, with 47 per cent of the votes each. That same poll gave Mr Trump a 12-point lead on the terror question in May.
A survey released last week by Quinnipiac University even gave Mrs Clinton a two-point edge (49 per cent to 47 per cent) on who can better keep the US safe from terror.
Observers say the results are potentially tied to the fact that Mr Trump's conduct had led around 60 per cent of Americans to conclude that he does not have the temperament for the White House.
Dr Barbara Perry, director of presidential studies at the University of Virginia's Miller Centre, told The Straits Times before the New York blast: "If you had asked me a few months ago, I would have said a terror attack would be better for Trump. Lately, I'm not so sure. I think some people might be afraid of his unpredictability."