They were too far in the future

John F. Kennedy would be resting comfortably in the rear seat of his limousine in Dallas, perusing his smartphone. He'd be reading the news, watching videos, or communicating with others on social media. Suddenly, his phone would be inundated with texts and alerts that an assassination attempt was planned against him. Of course, he would not believe such a thing was conceivable and would have no idea that his life was in risk. But, if their automobile had been assaulted, he would have had enough time to click a button on his smartphone, which would have sent a signal to a special server at the CIA, which would have promptly dispatched a rescue team.