If I were the US government with aspirations of complete population control, I'd be using the NSA data secretly to build a database of every single person, and

If I were the US government with aspirations of complete population control, I'd be using the NSA data secretly to build a database of every single person, and producing a "risk/threat score". Every action you take online will alter this score. Every person they are connected to would influence their score, not unlike Google PageRank. Slowly you build up a picture of every single citizen, and anyone visiting the US would also be subject to this, possibly triggered by a visa waiver program application or a visa application. By the time you land on US soil and your passport is scanned, the immigration agent will simply be warned that the traveller requires x, y, and z actions to be carried out. I'll get my tinfoil hat out now.