An unprecedented event that neither side could have planned for has come to dominate this year's US election like no other issue- COVID.
At the White House, sceptical of scientists' warnings Donald Trump's first reflex was one of denial.
"Now, the virus that we're talking about having, a lot of people think that goes away in April with the heat, as the heat comes in. Typically that will go away in April"
Trump introduced partial travel bans on China and Europe, but dismissed the need for wearing masks. Unlike his rival, who was rarely seen without one
And his administration's message on social distancing was at best mixed; supporters often mingled closely at presidential events
In contrast, Joe Biden's public appearances manifestly respected the rules; a clear political statement as the crisis deepened
The candidates also differed on lockdown.
Biden advocated the move sooner and for longer. Fearing the economic impact Trump resisited and when it became inevitable, he wanted states to reopen as soon possible, saying it was doing more harm than good. Biden lamented a lack of leadership, as he saw it.
"We've lost lives. We've lost businesses. We've lost paychecks. And now, thanks to Donald Trump's bungling, we may lose some of the progress we've begun to make."
While Biden remained cautious, Trump promoted certain drugs that scientists didn't wholly endorse. And, like many, he was stunned by the president's remarks on the potential use of disinfectant.
"Then I see the disinfectant which knocks it out in a minute. And is there a way you can do something like that with injection inside or almost a cleaning?
From the outset - and against the prevailing scientific consenus - Trump told voters a vaccine would soon be available. It would likely have boosted his re-election hopes.
Instead what he got was the virus itself.
Yet this didn't change Trump's approach to the pandemic, rather he portayed his recovery as a personal triumph. But by that stage much of the electorate had already made up their minds on his handling of the crisis.
And it remains to be seen exactly how that would reflect in the outcome of the polls.