They aren't allowed to collect the data directly...so they have the other UKUSA/5eyes do it for them with what used to be call ECHELON. There are supposed to be restrictions on that but it is hard to tell from the outside.

You aren't wrong but the misuse is within the bounds of what you are saying. They only need to make a reasonable effort to avoid directly surveilling conversations between two Americans if there's evidence available they are both Americans. They collect until they realize both parties are American and from what I understand those communications after the realization are not purged.

Additionally if you are speaking with foreigners they are also authorized to collect. The idea is that they can only use it for intelligence purposes but those data sets including domestic communications which were collected 'by accident' are exposed to the FBI for counter intelligence reasons. The problem is that the FBI has notoriously abused this and run searches against the database for domestic individuals for reasons other than counter intelligence.

https://www.eff.org/deeplinks/2023/04/internal-documents-sho...

Regardless of their formal categorization, they're a subset of "cop", which means they're not held accountable for misbehavior.

Furthermore, their misbehaviour couldn’t even be tried in a normal courtroom, even if there was mass public and political support for such an action.

They’d have to be tried in a secret FISA Court.

Before Congress would be possible depending on how much media attention arose