I agree the physical situation of the US is very advantageous. It would be difficult to conduct another invasion or full scale military attack. I've been thinking that this is one of the pillars for american exceptionalism. which is why 9/11 was such a big deal despite objectively being tiny chips.

But another attack of that scale seems possible, especially as the basic functioning of the State crumbles. Even a series of them if well coordinated. With 9/11 it was very "lucky" for USA because the whole response was just sitting there already planned out, waiting for such an event to be set in motion if such a thing ever occurred even though the CIA/FBI/NSA "didn't want it to" and "were protecting against terrorism".

If it were to happen without such plans ready, without such "not knowing in advance", I wonder what would happen. Eventually, somebody has to do it. Oceans can't protect forever.