You have 2 major conventions happening on the east coast, in major metropolitan areas..
Much of the nation's resources are going to be devoted to protecting everyone there..
I would be watching large gatherings of people and large metro areas in the rest of the nation.. Miami, Houston, Dallas, St. Louis, Kansas City, Chicago, San Francisco, Los Angeles, Seattle, etc...
Look for any large gatherings, or conventions, demonstrations, concerts, taking place in any of those large cities, and you are looking at a perfect target on those two dates..
All security is focused on Boston or New York, so hit where there is no security..
I would add to your post: to watch dates. Dates seem to have specific importance to Islamofascists. heck, Even Louis Farrakhan and his "number 19" bizarre interpretation of 'racism" at a particular event had "meaning". To keep the "terrorist base" (ugh) fervently motivated, an intrinsic "religiosity" meanintful to the group must be enacted. Simply bombing the US election conventions would just be - striking at a group of US politicians and their supporters. Okay, then what? But if the attack also occurs on a day or "holy day" important to the terrorists, they, in a word, get to experience a type of "holy flame" which fuels their appetites for MORE.
the amazing thing is the focus we have on nukes.
my concern is coordinated food borne biological attacks... by the sleeper cells working in our food supply. especially the fast food "mega warehouses" where tons upon tons of hamburger and pinto beans are stored and shipped to every city in america.
I don't think the food supply is as safe as we tell ourselves it is.
My guess would be much closer to election time so that the administration does not have time to recover. If one presumes that the goal is not only to terrorize, but also to affect the outcome of the election, I would expect a multitude of small attacks in predominantly strong republican areas designed to keep people away from the polls on election day. I would also suspect a communication instructing America to bow to UN authority or something more serious would follow.
Just my 2 cents.