The downfall of the US can happen in two ways, though I don't pray for it:

Weakening the US politically, and ending the USD's dominance in global finance.

Trump is currently taking care of the political aspect, his actions keeps dividing the US, inciting violence, undermining unity, etc. All these serve to undermine the political integrity of the great American Republic.

The dethroning of the USD is already being hastened, also by Trump's ill-advised decisions! Imagine ships passing the Hormuz Strait not having to pay for passage in USD. That's just a seed that can help inspire other countries to trade in local currencies. And, in my humble opinion, Trump is fully to blame.

He came to make America great again, but unfortunately it's the oppoosite.

When I first heard of MAGA, I thought: How stupid. How do you want to make a country that's a global superpower and the number one nation in almost every aspect, great again? It's already the greatest nation on earth at the time you assumed office.