The machines record without human involvement 24/7 everywhere. They are always on.
If NSA humans listen or watch the recordings, it is done by warrant for US persons inside US jurisdictions. For all other persons, a warrant is not needed.
US persons inside US jurisdictions have protections by law.
Not if you are talking with someone not covered by the Constitution which its why we have FISA courts. Once they have access to anything they can and do read it maybe they can't use it in court but they certainly do use it to find ways to gather information they can use in court. Easier to find something if you know what it looks like.
The real power in DC today is in the hands of the person/people that have the black book of pedophiles that Maxwell has.