I can't cover in detail but in general a fisa warrant is to intercept the foreign person. It is a given that the person on the other end may often be an american- in which case you have to mask out their identity. It is also a given that sometimes through the fisa warrant surveillance that you uncover or suspect illegal activity by the american who was on the other end of the conversation. That's fine but once you start monitoring the americans conversations with the expectation that you are surveilling them - rather than or in additiion to- the foreigner- then the government needs to get a normal Article 3 criminal court warrant because they are americans. If you don't do that, then it is illegal and the fruits of the monitored discussions are therefore not admissable- including follow on investigative work which was set in motion by the illegal tapping. If the government can still prove their case without all that, then they are free to do that, and sometimes the government can if it has multiple efforts in motion and they are able to show that they still would have discovered it through their other efforts which were legal and still would have been launched if the illegal tapping had not been done. Those are the issues. It is for their lawyers to make sure how their facts line up against the law. Also, flynn and mannafort can not necessarily be lumped together. Keep in mind what my position is, I am just saying that mueller has done his little shock and awe routine to make mannaforte cave but mannaforts lawyers get to have a strategy too.
I can't comment further right now, but no, when I refer to the unmasking issues I am referring to the unmasking machine that powers and rice were running. A sudden major increase right before the election- and involving trump associates among them. Follow that development for more on it.
