The ACLU Is Arming Lawyers to Expose State Surveillance Secrets

Not from the US but the ACLU did a lot of good also for people outside the US. More recently it seemed to have lost its way with some focus on "modern" activism, and yes I do mean foul compromises regarding to freedom of speech mostly, but not exclusively. No idea how to explain that better. Glad it is back to business here. I hope this isn't another partisan move that will stop as soon as the players in the white house change again.

That's covered in the article, along with a bunch of other things I had no idea about.

I'm not a lawyer either, but what you're referring to is called parallel construction, and it's not legal. Basically it comes down to 4th Amendment protection against unreasonable search. You can't use methods that violate the 4th Amendment to discover someone has done something wrong, then launch an investigation which uncovers evidence in the traditional sense. The whole process is poisoned because with the illegal means, they would have never had a reason to investigate. You can't just go fishing for criminals or else we are basically all considered guilty by default. The problem of course is that this does happen, and the prosecutors just lie, ommitting the source of the original evidence.