Donald Trump's positive COVID-19 test has thrown the US into turmoil.
The President was scheduled to appear at multiple rallies and debates in the lead-up to the election on November 3 - all of which will now need to be put on hold.
But who will lead the country if Trump falls seriously ill, especially so close to the election?
Trump's physician has issued a notice saying the President will carry on with all his duties as he recovers - however COVID-19 is unpredictable, as the world saw when UK Prime Minister Boris Johnson was put in intensive care in April.
Should Trump fall seriously ill, then it follows that Vice-President Michael Pence would take over his role.
But seeing as Trump's positive result is likely linked to that of two prominent White House aides - one of whom was Pence's valet - contracting the virus, it is not unthinkable that Pence would also fall ill.
If this happens - the US could face a constitutional crisis.
The law provides little clarity on such a scenario. Article II of the Constitution lets Congress "provide for the Case of ... Inability, both of the President and Vice President, declaring what Officer shall then act as President, and such Officer shall act accordingly, until the Disability be removed."
That law still stands, and it puts the Speaker of the House first in line. By this law, Nancy Pelosi would lead the country.
But Article II does not provide any way of determining "inability" - so if Pelosi, believing Trump and Pence are too sick to fulfill the duties, declared herself acting President and either man contested it, the White House would be hurled into uncertainty and the new acting president would struggle for legitimacy.
Courts could settle the matter, but time would be of the essence as it would leave a power vacuum at a time when the US is suffering civil unrest.
The poor handling of the COVID-19 crisis, coupled with large-scale protests over systemic racial inequality sparked by the deaths of African-American citizens at at the hands of white police means the country is akin to a tinder-dry forest - and a presidential contest could be the spark to set it alight.
On top of this, if Pelosi was to take over, she would need to resign from her position as Speaker because of the Constitution's obscure incompatibility clause, which says that "no Person holding any Office under the United States shall be a Member of either House during his Continuance in Office."
All in all, it would be a confusing change to navigate - and Congress, not known for it's swift dealings, would need to handle it quickly.
But this is all hypotheticals - as it stands, Trump and his wife Melania have tested positive but Pence is still clear.
Now, all the White House can do is ensure staff are washing their hands and wearing their masks as they wait to see what unfolds.