The last time President Trump and Joseph R. Biden Jr. debated each other, the nation was left grappling with Mr. Trump’s attack on election integrity, his refusal to categorically condemn white supremacists and bitter exchanges of a type rarely seen in American presidential politics.
That was last week.
Now, in a stark reminder of the tumultuous nature of the 2020 race, all of those issues — which are of significant importance to American voters — have been eclipsed in the political dialogue by a fight over health precautions and transparency that is set to define the next presidential debate, scheduled for Oct. 15.
Mr. Trump, who has tested positive for the coronavirus, has insisted that he is “looking forward” to the debate in Miami, despite great uncertainties about what his condition will be then. Mr. Biden and his team, for their part, are seeking to place the onus for a