We already wrote about the Privacy and Civil Liberties Oversight Board (PCLOB) and its scathing report as to how the program to collect phone records on pretty much every phone call in the US was both illegal and unconstitutional. However, if you don‘t want to get too down in the weeds over why it‘s illegal, the absolutely best summary I‘ve seen comes from Julian Sanchez and fits into a tweet:

215 allows FBI to get records relevant to an investigation. PCLOB: NSA program fails on „FBI“, „records,“ „relevant“ & „investigation.“
— Julian Sanchez (@normative) January 23, 2014

In case you can‘t read that, it says:

215 allows FBI to get records relevant to an investigation. PCLOB: NSA program fails on „FBI“, „records,“ „relevant“ & „investigation.“