One of the things that pops up in quite a few AHs is the invasion and conquest of the United States by a foreign superpower (generally a surviving Third Reich or an gigantic Soviet Union). However, many of these scenarios have problems in their logic (namely that the USA could nuke the aggressor nation into dust in a heartbeat). So, what I want to know is: is there any way that a United States in 1950 or later could be invaded without the invader being destroyed in the process, and how?