The US now has "little doubt" the Syrian government used chemical weapons against civilians last week, a senior reporter told Reuters. The Obama administration said a "serious response" would be required should evidence of such an attack emerge.
The CBS White House correspondent Mark Knoller has tweeted that the White House is refuting claims of intervention in Syria.
The Democratic presidential candidate may also have shown his cards on his choice of running mate.
The US president also shared a post on Twitter accusing Dr Anthony Fauci of misleading the public over hydroxychloroquine.
Fears over an impending second wave of coronavirus dominates Wednesday’s front pages.