The blackmail information doesn't need to be passed to a third party. It can be brought directly to bear on problematic government officials by the NSA.
All they would need to do is make the senator understand that a record of all correspondence and browsing history exists.
Considering about 5% of the population has some pedophilic tendency, and estimates are around 10% of people have an incest fetish, 10% of people are estimated to be gay yet only Tammy Baldwin is out in the senate, lots of successful people do drugs, and everyone else has tons of relatives who may or may not have those problems, you can not underestimate the power wielded by someone with access to all our communications.
It's too great a power to comprehend. And someone wouldn't even have to be consciously doing ill to exploit it. I imagine that anyone in the position would believe they're protecting the USA from terrorism, and righteously punishing the deviants by leveraging their 'sins' while unconsciously building the infrastructure for future tyranny.
Furthermore, I've only listed the problems I think could be discovered through software. We aren't getting into conspiracy theory stuff like what would happen if you put a secret team of 10 analysts and 20 lawyers to work for a year looking to find laws broken by the members of the legislative branch. I mean, Hoover has been dead for a while, right?
