The thing is that all those territories are already "US" in the same way as Hong Kong is China. Marching in with soldiers and planting more American flags there is not expanding the US empire, it's at most consolidating and reshuffling offices within the same country.
That doesn't mean China shouldn't maximally extract value from the internal US conflict, encourage independence from US and make these areas into quagmires. And especially Mexico with all those insane cartels in there are just waiting to be used to make life unpleasant in the US core home areas.
Yeah, but this is not only about how little the resources were spent on those acquisitions, but also about the loss of focus too.
Imagine instead of brainstorming and working toward coercing Canada to formally join the US, coercing Denmark to sell Greenland, and planning to launch an attack on Panama and Mexican cartels, the next US presidency actually focused on what's 1000 times more important and salvaging something domestically first.
However, their bullshit political system is only about what sounds good, not what's actually best. That's why it never had any future to begin with and it was only about luck and fate that they have come so far.
What's the point of incorporating Canada and Greenland, looking large on the map, and then fragmenting in 3 years for example in civil wars?
I have seen no PLANS from Trump yet to take on the corrupt MIC, cancerous media, coerce oligarchs on how to ACTUALLY move manufacturing back, reform the social and pension system, how to build infrastructure, how to educate more engineers, etc, but I have seen him talk about BS.
I have seen him talking about Greenland, large borders, and megalomania only. The opportunity cost is huge even if actual is not.