...With other nations closing the technology gap the US is increasingly vulnerable to the shear size of potential adversaries forces.
Because it would be just so easy for China or South Korea to ship millions of soldiers across the Pacific ocean (I assume we'd just sit there and watch it for weeks, doing nothing). And then we'd sit around while they established a beach head in California, landing all those millions of troops and getting them organized after all that time at sea (seasick, questionable food etc makes soldiers ill).
You know what, I bet we could even just do that. We probably could utterly ignore them until they got all good and solid setup in California, ready for the big march to the Atlantic, and still every soldier and American with a gun (a lot of us) would rush to the front and push them back into the ocean...
Don't be silly, those big number armies are nowhere capable of hurting mainland USA. The issue is more about flexing regional power on the Korean Peninsula, in Taiwan, and Japan. Right now the USA is the only nation capable of projecting power as we do in Asia, halfway around the world. Its going to take a huge effort by the Chinese to get even close (they've spent years and billions and still can't even really challenge the US in their own backyard...) and just forgot about North Korea. They will never project power beyond the edges of their border and maybe a bit into South Korean (however far those SCUDs missiles can fly really).