They who? It is perfectly valid for the NSA to buy that data, because the NSA cannot use that data in a way that violates the fourth amendment without breaking

They who? It is perfectly valid for the NSA to buy that data, because the NSA cannot use that data in a way that violates the fourth amendment without breaking other laws. If the FBI buys that data they need to have probable cause prior to that purchase else all the purchased information and everything resulting from that information cannot be used to prosecute cases. The reason is because defendants have a legally established expectation of privacy on certain electronic communications such as email.