I agree with your identification of catastrophes to come, but I'll just add my view, which you already know I think, and that is: you're right, the worst will happen regardless of who's in the presidency. I believe because it is ecological overshoot driving the bus over the cliff. EO is causing the collapse of the biosphere in several regards right now, in real time. That will, with history as my guide, lead to social disorder, war, hunger, disease and more. There is no stopping it, because it is a state of affairs, not merely a process*. There is no technological fix—technology itself is what brought us to our current height (8 billion people x desire for a Malibu lifestyle).
Anyway, I digress into the whole point of my Ecological Overshoot thread.
Worse that can happen under Harris is that she, like the rest, simply cannot accept the truth of EO, or the necessity of leading an orderly and humane downsizing of the American economy to a sustainable level. Worse that can happen in the next six months? A contested election being handed by installed electors to the House.
/rant
*Think Titanic, the movie, when the ship's architect tells the captain the ship is going to founder, "She's made of iron, sir, I assure she can, and she will. It is a mathematical certainty."