Tom Clancy wrote a book 'Teeth of the Tiger' that includes such a scenario. The shopping center/mall is one I'm familiar with and I've never quite gotten over that book .... it was very real to me. The terrorists also came in through the southern border.
IMO it's a matter of 'when' .... and while we're talking 'horrific', what if instead of a mall it's something like Beslan?
These Kenyan Mall shooters are probably the ones who did Sandy Hook. They’re Americans, right? Any from Connecticut?