I have read articles and other data about the idea of other major nations growing in North or South America. Two mentioned names were Mexico and Brazil. Anyone have a take on this. Would our influence in the Hemisphere be threatened?

I think it would depend a lot on the nature of the “threat” that’s in the perceived “backyard”.

The priorities of the government would be heavily influenced by economic impact. Certainly a military threat would require a military response. Anything else, we can just speculate to the end of day until we know what the specific threat is.