WASHINGTON • Picture this: It's the week before Christmas and Americans are glad to have put what has been a bleak, poisonous year of presidential campaigning behind them.

While the race turned out closer than most had imagined, the polling ultimately proved correct and Mrs Hillary Clinton edged out her rival, Mr Donald Trump, to become the first female president of the United States.

Suddenly, there's a new bombshell from the Federal Bureau of Investigation (FBI).

After looking into the new trove of e-mails found in the laptop belonging to top Clinton aide Huma Abedin's estranged husband, Mr Anthony Weiner, investigators concluded that Mrs Clinton is guilty of criminal wrongdoing.

What happens then? Does that disqualify her from taking office? And what if it happens after she has been inaugurated? Could a sitting US president get sent to jail?

These and a multitude of other questions were raised this week, thanks to the vague three-paragraph letter from FBI director James Comey telling US lawmakers that the bureau was taking "appropriate investigative steps designed to allow investigators to review" a trove of newly-discovered e-mails.

The letter offered little context as to their potential significance apart from saying that they appeared to be "pertinent to the investigation" into Mrs Clinton's use of a private e-mail server while she was secretary of state, and gave no timeline for the investigations.

That sent legal scholars and historians trawling through the books to try and understand the many implications. But there are few clear-cut answers.

Much ambiguity arises from the fact that the situations Mrs Clinton might find herself in have no precedent in history.

If Mrs Clinton wins the election but gets charged before Inauguration Day on Jan 20, most experts think she will likely step down and hand the presidency over to her vice-president, Mr Tim Kaine. PHOTO: AGENCE FRANCE-PRESSE

And though it may all come to nothing - no one yet knows if the e-mails are even new material - the potential for adverse outcomes for Mrs Clinton are many.

COULD CLINTON GO TO JAIL?

Perhaps the most obvious pitfall for Mrs Clinton is the worst-case scenario: She gets charged with a crime and is convicted.

Could she go to jail? The consensus answer has been theoretically yes, although she probably won't.

One challenge in answering this question is that it has never been clear what crime Mrs Clinton could be charged with. There were no charges filed during the previous round of investigations and the FBI letter did not make clear what offence it is looking into.

Most experts are focusing their attention on Provision 793 (f) of the Espionage Act, which makes it a crime for an official handling classified material who "through gross negligence permits the same to be removed from its proper place of custody or delivered to anyone in violation of his trust, or to be lost, stolen, abstracted, or destroyed".

While Mr Comey had earlier described Mrs Clinton as "extremely careless", it is not immediately clear that her use of a private e-mail server permitted it to be removed from its "proper place of custody".

As University of Texas law professor Steve Vladeck recently wrote in Slate magazine: "It certainly appears to be focused on government employees who dispossess the government of classified material (like a courier who leaves a satchel full of secret documents in a public place). But how much further does it go?"

Someone guilty of violating that provision could be sent to jail for up to 10 years. Hence, that is a fate that cannot currently be ruled out for Mrs Clinton.

But what if it were not Mrs Clinton, the ordinary citizen, that gets charged but Mrs Clinton, the president-elect or president?

COULD SHE STILL BECOME PRESIDENT?

If Mrs Clinton wins the election but gets charged before Inauguration Day on Jan 20, most experts think she will likely step down and hand the presidency over to her vice-president, Mr Tim Kaine.

Nothing in the US Constitution disqualifies someone from becoming president, whether they are charged with or convicted of a crime.

But the prospect of having a president charged with a crime would be so politically unpalatable for voters that a president-elect would most probably step down in favour of the vice-president-elect.

A similar sort of mechanics would be in play if - unlikely as it seems - the FBI and the courts operated so swiftly that a president-elect is sentenced to jail time before being sworn into office. In that situation, the imprisoned president will likely be deemed incapacitated and the Constitution then puts the vice-president in charge.

If, however, any possible charges do not get filed until Mrs Clinton is inaugurated as president, then things get more prickly.

There is some ambiguity and disagreement about whether a sitting president can be prosecuted for a crime, but many legal scholars believe that a president, as head of the executive branch, is immune from federal prosecution.

Any such action would have to take place after the president is no longer in power.

That brings up the question of impeachment. "Assuming she wins, and the investigation goes forward, and it looks like an indictment is pending, at that point in time, under the Constitution, the House of Representatives would engage in an impeachment trial," Texas congressman Michael McCaul told Fox News. "I would hate to see this country being thrown into a constitutional crisis because of Hillary Clinton's behaviour."

Such an action would have no precedent in history. The US Congress had in 1873 concluded that office holders could not be impeached for crimes committed before they came into power. While that appears to preclude Mrs Clinton from any sort of attempt at removal while in the Oval Office, it isn't a sure thing.

Congress' 1873 decision is not a binding precedent and nothing in the Constitution explicitly prevents Congress from commencing impeachment on actions that preceded a president's time in office.

Given the current political climate, it will surprise no one if Republican lawmakers decide to defy tradition to try and remove a Democratic Party president.

PARDON ME, ONE LAST THING

Then there is one final wrinkle that could nullify any such threat to a Clinton presidency: a pardon from President Barack Obama.

American presidents have wide-ranging powers to grant pardons for crimes, even in instances when no charges have been filed.

A good example was the move by President Gerald Ford to pardon former president Richard Nixon for his involvement in the Watergate scandal.

Investigations then had revealed a comprehensive cover-up of a host of White House-sanctioned illegal political activities, including wiretapping the Democratic Party offices.

Mr Nixon resigned after it became clear Congress was very likely to impeach him. But he escaped the possibility of facing criminal charges because of President Ford's deeply controversial pardon for all offences Nixon "has committed, may have committed or taken part in" during his tenure as president.

If it becomes clear before Mr Obama leaves office that Mrs Clinton is headed for legal trouble, he could very well protect her with a similarly blanket pre-emptive pardon.

However, the move may exact a political price on the party, and would likely make most voters assume Mrs Clinton is guilty.

The best outcome for Mrs Clinton is, of course, simply for the FBI inquiry to turn up nothing.

But the cloud of uncertainty looks set to hang over her long after the result of the presidential campaign is over.