Are there recorded instances of sabotage in the United States mainland during WWII from either the Germans or Japanese? If so, are there demographics to backup the saboteurs and their nationality and/or heritage?
The major attempt was Operation Pastorious. When the continuously and possibly intentionally inept German Abwehr Intelligence Agency sent 8 Saboteurs aboard 2 U-Boats to the US to bomb rail lines, dams, and power plants in June 1942.
It was a failure, the leader of the ring went to the FBI, along with a member who had spent time in a Concentration Camp and had no love of the Nazis. All 8 were rounded up, the 2 leaks got Life in Prison, the other 6 the electric char after a military tribunal.
All the men were German nationals, but had spent time in the US and were fluent in English, 2 also held US Citizenship.