Seems like the safest bet would be to fully inventory every human, know everything about them as well or better than they do, and then, once you're highly assured of their safety to the commonwealth of the country monitor them for even the slightest changes in their disposition or regular pattern of activity.
Of course, you would have to completely disregard any concept that people would have a freedom to privacy to do that, and you would also have to account for natural changes over time.
People make new friends, get exposed to new ideas, and gradually change no matter how hard you try to lock them in a box. The data storage and processing requirements to monitor America's 350 million people would be understated as staggering, the man hours for perfect enforcement incalculable, and even if you reached Pareto parity (monitoring 80% of the highest-risk individuals 100% of the time) you're still going to have people slip through the cracks.
I would place a $100 bet on this already being the practice of the 3 letter agencies and if they haven't fully rolled it out I would hazard an extra tenner on that they're within 5 years of completing it as long as their funding isn't disrupted.
The only defense most of us have against it is that we're not individually interesting so we probably never register as more than a blip on a hard drive somewhere under most circumstances, human eyes never prying into the worlds we make for ourselves.