They will come up from Mexico—hit Texas— Houston is my bet—at least thats what my Ouija board Says.
I can see Houston being a target - their paymasters really don’t like their stranglehold on oil being threatened, but think LA, SF or Galveston would be more likely, from a couple of standpoints.
They are far easier to get into. All port cities, and, for the poster who has discussed the unlikelihood of a nuke, a large fuel/air explosion is nearly as devastating. A container ship or tanker converted to a floating bomb would wipe out much of the city - or a certain landmark bridge - quite easily. Look up the Grand Camp for an accidental version of this.
LA is, of course, the home to the culturally imperialistic den of sin called Hollywood, which they hate passionately, so might be most likely, with these truck thefts being a diversion.
Pure speculation, of course. My SiL in the police here in the UK has said that all emergency services have been quietly put on standby alert for the day - all leave cancelled.
Stay safe!