He's lost support among college-educated whites who historically vote more frequently than the African American and Hispanic voters who he's spent a lot of time courting.
From Cook: "In an average of nine live-interview national surveys conducted since the start of June, Biden is clobbering Trump 58 percent to 37 percent among whites with college degrees, more than double Clinton's 51 percent to 42 percent lead among that group in 2016 according to the Cooperative Congressional Election Study, a nationally representative sample of 64,600 adults."
I don't mind the minority outreach but as the Dem Party knows all too well, minorities do not turn out for elections with the same frequency as white voters. Trump needs both college-educated and non-college educated whites to turn out for him.
Biden is a disaster of a candidate, on par with Hillary. But Trump is still behind, which is why Biden is in his basement and not on the trail.
Trump has work to do.