I mean, imagine for a moment that Russia or China were to spend a few tens of billions of dollars on a cluster to run an AI.
They have the human capability to ensure that it is state of the art in all current ways, and could theoretically use some processes that aren't disclosed to the public. I don't think anyone would say that China at least doesn't have the brainpower to do something like that.
Then, these government leaders could ask the AI to come up with simulations on how to conquer the world.
The AI would probably say something like, "America has to fall, since it's military might is the strongest resistance to your ability to dominate the globe".
How would you do that?
Ensure weak or compromised politicians get elected, which will make the American people lose confidence in their government.
Spend resources to ensure that the financial stability of the country is negatively affected. Do this by disrupting the flow of goods into the country, viciously competing with any product based company of any merit, and purchasing housing in the major financial centers of the country.
This serves three purposes:
1: Businesses will become tight-fisted with their spending wherever they can as they won't always know if they will be able to purchase the goods they need when they need them. The easiest way to reduce spend in the short term is to underpay and overwork your employees by firing the more expensive employees and shifting their workloads to others, so that will be the first thing that happens.
2: The smarter and capable people will attempt to escape the rat race by relying on their inventiveness. They will suffer in drudgery for years while they perfect a product that someone needs and is willing to pay for, and then, since manufacturing in America is ridiculously expensive thanks to China's price competition, they will outsource the manufacturing of their product to China. This will happen frequently, and they will be taking all of the risk for themselves.
Once they have a successfully tested product, China will clone the product and flood the market with inferior quality but massively cheaper clones, ensuring that the original business never achieves the success it could have and then has to cut costs, putting the employees of that company into the same conditions that the founder started the company to escape.
3: Housing will become very expensive, so the citizens will not be able to afford the same quality of housing that their parents did. This will further increase their unhappiness and destabilize the power of America.
Once all of that is done, then you let the kettle simmer for a while. Spend the money, time, and energy to keep the pressure up. Use the time to buy or subvert more politicians.
When this is done, the country will be weakened by its internal stresses and so charged that all it will need is a single strong event to vent all of that pressure on. A match to a powder keg will blow the whole thing up and America will collapse from civil war.
While that civil war is going on and the whole world is watching, launch your attacks. Take over your neighboring countries. Threaten nuclear annihilation on anyone that stands against you as within a few years you quadruple the size and power of your country.
By the time America pulls it's head out of the fog and realizes what is going on, it will be too late.