In the name of national security, often behind closed doors. Even if the funds are there to hire competent defense, which most of the time they're not, you're fighting an uphill battle.

A fact doesn't need to be usable as evidence in court to be usable for blackmail.

Anything that can make your life harder will do. They can find something that:

- will put a you in a difficult position with friends and family

- break trust in a business relationship

- destroy your reputation in regard of the public

- trigger costly investigations from a 3rd party

- pressure you and take your energy, moral, money, time and health in the process

How would you defend in front of FISA court?

https://en.wikipedia.org/wiki/United_States_Foreign_Intellig...

It's more than some cases, and yes it can be done at scale, to some extent: https://www.reuters.com/article/us-dea-sod-idUSBRE97409R2013...

That simply is not true. In most "Terrorism" cases there is always major restrictions on defence lawyers both accessing and challenging prosecution evidence. From the bullshit of Gitmo to Secret Trials in most Liberal Democracies, in the field of "National Security" lies are the norm.

Blackmail by definition isn't used in court.