The US doesn't need to prove to the world that a bad president will never be elected again, which as you say is probably impossible and definitely false. What the US can do to rejoin the world in something akin to its former capacity is to walk back the extreme levels of authority granted to an individual who changes every four years (why is the executive able to change tariff levels every day?) in a way that relatively elevates rule of law and deliberative, compromising decision making.