With the US the worst-hit nation by the global coronavirus pandemic and in the middle of an election campaign, the news that its leader, Donald Trump, has also contracted the virus will be unsettling for many.

Mr Trump is not the first leader to have tested positive to the coronavirus – British Prime Minister Boris Johnson and Brazil’s President Jair Bolsonaro have also had it and recovered.

But it comes at a difficult time in the US and as the traditional leader of the Free World, it raises a number of questions about what this means for the country.

Donald Trump and Melania Trump have tested positive for COVID-19. Photo: Getty

Here’s what we know about the process surrounding a president who becomes ill and whether this has happened before.

Who will be in charge?

It’s still early days and the President’s doctor says he will quarantine at the White House with his wife Melania, who has also tested positive.

Tonight, @FLOTUS and I tested positive for COVID-19. We will begin our quarantine and recovery process immediately. We will get through this TOGETHER!

— Donald J. Trump (@realDonaldTrump) October 2, 2020

He may experience a mild case and be able to continue his presidential duties and recover within a few weeks. So at the moment, Trump is still in charge and given he’s still tweeting, you can assume he’s well enough to do government duties.

But if the President were to become very sick with COVID-19, then there is a process in place.

What would be the process if the President were to become really sick?

When this came up some months ago, some suggested that if the President did get the coronavirus, “depending on the severity, the 25th will have to be invoked on physiological grounds”.

The 25th amendment of the constitution allows an orderly transfer of power if the president can’t execute his duties.

“In case of the removal of the president from office, or of his death, resignation, or inability to discharge the powers and duties of the said office, the same shall devolve on the vice-president,” the Constitution states.

Has there been a precedent for this?

It’s only been invoked a few times – always voluntarily by presidents when they have been put under general anaesthesia for surgery.

In those cases, the vice-president assumed powers until the president woke up, when the order was rescinded.

The order of succession is clearly laid out in the constitution. Photo: Getty

For example, in 1985, then-vice-president George HW Bush took on Ronald Reagan’s duties for about eight hours while Mr Reagan underwent an operation on his colon.

But if a president suddenly became incapacitated or fell into a coma, his deputy and a majority of his cabinet members can remove him from office.

They would simply write a letter stating that the president was no longer capable of executing the duties of office, and send that to House Speaker Nancy Pelosi and the Senate pro tem, Chuck Grassley.

Then the vice-president “immediately” takes on the president’s “powers and duties”.

What would happen if both the president and the VP became incapacitated?

There’s no suggestion that Vice-President Mike Pence may also have COVID-19.

But given the coronavirus has reached Mr Trump’s inner circle, it’s still unclear just how many people he came into contact with before he tested positive to COVID-19. So this question may come up.

The US Constitution has mapped out what happens in the worst possible scenario.

After the Vice-President, the next person in the line of succession is Democratic House Speaker Nancy Pelosi.

Democratic House Speaker Nancy Pelosi would be the next person in the line of succession after the Vice-President. Photo: Getty

After her, it would be Republican senator Chuck Grassley, who, as the longest-serving member of the majority party, has the title of pro tempore.

If all those offices were vacant, then the president would be the Secretary of State, followed by the Treasury Secretary.

This has only happened on the fictional TV show Designated Survivor, when an explosion during the president’s state of the union address left the secretary of housing (13th in the line of succession) in charge.

How will this impact the election?

It’s still too early to say.

At this stage, Mr Trump will be unable to leave the White House to attend rallies for a couple of weeks.And the timing is less than ideal, happening just a month out from the US election. This is a crucial phase of the election campaign and will divert the conversation around the campaign to the coronavirus pandemic.

Mr Trump has attempted to deflect from the issue during the campaign, with Democratic presidential nominee Joe Biden frequently criticising the President for not having a clear national plan to tackle the pandemic.

-ABC