I dont see anyone that could. Even a weakened US is likely to have nukes, and a fair few of them, a hypothetical invader that is not Canada or Mexico (which would have to deal with having a smaller population and a much worse economy, or a much smaller population) has to deal with crossing an ocean and therefore building an extremely large naval capability. And finally, whoever it is would have to occupy a huge area with a population of over 300 million.
I dont see anyone that could. Even a weakened US is likely to have nukes, and a fair few of them, a hypothetical invader that is not Canada or Mexico (which would have to deal with having a smaller population and a much worse economy, or a much smaller population) has to deal with crossing an ocean and therefore building an extremely large naval capability. And finally, whoever it is would have to occupy a huge area with a population of over 300 million.