In the final stretch, Hillary Clinton and Donald Trump are going all in — campaigning hard in the battleground states that will decide this election. Although Clinton’s lead in the RealClearPolitics polling average nationally ranges roughly between 4 and 5 percentage points — a seemingly comfortable margin with less than two weeks to go — both camps are keenly aware that politics can be unpredictable.

One possibility is that this election is tighter than the polls indicate. One potential factor being discussed is the “shy Trump voter” phenomenon. This is actually a theory, not a proven fact, but the notion that Trump has been marginalized by elites in the media has spawned a concern among Democrats — and hope among Republicans — that The Donald will outperform his numbers.

Then there’s the prospect of an “October surprise” that changes the equation at the last minute. Such a revelation occurred in 2000, days before voting, when George W. Bush’s old drunk-driving arrest was unearthed by a Fox television station in Maine. Bush’s vote totals almost certainly dropped because of this well-timed little bombshell. This year’s equivalent may — or may not — have come Oct. 28 when the FBI announced it is reopening the investigation into Clinton’s emails that she sent and received on a private server when she was secretary of state.

"In connection with an unrelated case, the FBI has learned of the existence of emails that appear to be pertinent to this investigation," FBI Director James Comey wrote in an unexpected letter to Congress.