[rtkwe]

There wasn't much of a Nazi spy presence in the US much less effective saboteur operations. One of the few people convicted for espionage had their conviction overturned because the information they passed was publicly available. The US was never under much direct threat, there were a smattering of attacks and raids on the West Coast but those didn't amount to much. Extreme distance was a better shield than any secrecy or military might, it's part of why the post war years were so good and continued for decades afterwards, the US was completely untouched and the rest of the (then) modern world was bombed to absolute smithereens.

https://www.neh.gov/article/nazi-spies-america