A simple setup is to leave local PDs in the dark as they can always ask for the FBI's help for serious cases. Then the FBI gets access to tools provided by the NSA that look innocuous. For instance, lets assume the NSA snoops enough TOR to do packet correlation attacks. Imagine a simple tool where an FBI agent can enter an IP address or two, and get a list of "associated" IP addresses. Each IP can then be followed as its own lead. Once you've found the needle in a haystack, it's very easy to construct a false narrative of how it was found.
Politically, I don't know how it's possible to look at the current climate and think it will work against mass surveillance. Politicians will just shy away from directly confronting the issue. Whenever any spotlight gets close, the agencies will continue categorize it as national security / tough on crime / etc. The best political ally is seemingly the judiciary, and that itself will only slow things down.
