Most of the world has an unstable government that does stuff like this every decade or two at least. If the US is going to be just as bad, everywhere is an alternative, although none of them will be as good as the US was.

There's tons of global markets to invest in, not just US, and of course other US investment instruments other than stocks if you feel those are more investable in current climate.

There has already been capital flight. Trump's (temporary?) U-turn on tariffs was due to a massive sell-off in US Treasuries, largely by the Japanese, which caused yields to jump.