We've heard this threat before, and they seem to keep popping up.
Some people will react with fear and sell off their stocks. Some will buy gold. All I can say is "good luck."
The US economy is the strongest in the world. Our population represents less than 5% of the world population, but our GDP is the highest and strongest. The reason the US stock market gets pushed up is simple supply and demand. Most people of money around the world know that the American economy is the strongest and most stable. China and Japan buy US bonds for good reason. It's stable, because our economy is based on many forms of products and services. It's not limited to a few like many countries.
Economics is not science. Nobody can predict how the economy will perform in the future. Anyone saying they can is a kook. They can't explain the when and whys. If they could, they would be so rich, they wouldn't need to be working or bothering with the stock market.