Does the NSA really need to have an agreed upon backdoor to have the ability to access the information they seek?
Getting access to it "voluntarily" makes thing so much easier. It says in the slides the PRISM program only costs them $20 million a year.
Now there is a system that can be used for example. That system is once NSA identifies the list of suspects they forward that record to a another agency (FBI?) who then is in charge of finding other evidence, which could have plausibly be found anyway, and prosecute based on that. They can never release the initial reason why they got "interested" in someone as that might reveal the abilities of the NSA.