Technically correct that it is not set in stone until the Democratic National Convention is held on August 17-20, 2020, but Biden is the clear leader and everyone else has dropped out, so he is the presumptive nominee. https://en.wikipedia.org/wiki/2020_Democratic_National_Convention
The recent past has drawn my attention Andrew Cuomo better than Biden but I usually categorize "what if" questions as a child's way to draw attention to their overactive imagination.