Not saying you're wrong, but how can such a large scale operation be brought forth without the leaking of information?
not sure, but the Israeli intelligence and defense agencies were certainly caught off guard...it's difficult to believe it wasn't intentional, given the security in place...could also be human error complacency.
9/11/2001 happened, and our collective security agencies "dropped the ball". I'm sure they'll fumble and fail again.
We have people in the US illegally of unknown origin. It would be easy enough to have 2-3 people sent to a specific part of a US city with contact between them; over time, send others there in small numbers, with means to contact one operative already there. So create a loose network in part of a city that has no knowledge of other loose networks in other parts of a city. A slow, gradual deployment would easily go unnoticed, and interactions between 2, 3 or 4 operatives may not seem anything more than friends. With large numbers of illegals throughout the country they could easily blend in with the crowd and go unnoticed.
Get several of these loose disconnected cells in place, then send in the coordinator that can contact someone in each cell / subgroup of cells within a city weeks or months before the event, to communicate the date/time to activate.
Let's not forget the border has been opened for many years; terrorists can't confront us directly with a large force, so they do the opposite, slow gradual infiltration, loose coordination. US security, police, border patrol, etc. could easily miss these activities.
I'm certainly not an expert, and no one is investigating how the 7-Oct attacks by Hamas were missed by Israel military and security.
I think many underestimate the drive, tenacity, hatred, focus and intelligence of these terrorist groups. Just look at 9/11, from a tactical planning perspective, it was a foreign attack on American soil not seen since Pearl Harbor that killed thousands.
I think terrorists are certainly assessing our blind spots and weaknesses, and will attempt to exploit them.