[BitWielder1]

Instead of a million troops attacking America at the border, they invade silently to later attack America from inside.
Same in Europe.

[Jonty30]

My working theory is that a well planned terrorist attack within can kill off 1000 people for every attacker. They don’t need to kill everyone, but just enough to turn counties which can turn states. Some states are purple enough that, with a small push, can become forever blue.