Now add to this the fact that NSA shares information with DEA and IRS (at least, that is what is known, who knows what else exists), and both are trained to lie about where the information comes from as a matter of routine, and that information, as any other, once shared can not be unshared - and you have a nice unregulated channel here.
NSA analyst makes a "typo" and finds information on John Doe that, say, IRS wants. He then "mistakenly overshares" this information. Once it is detected, NSA instructs IRS to immediately forget the information, which they happily agree to do, though miraculously it turns out they've got exactly the same information by other, confidential, channel. Thus, no abuse of NSA facility ever happened, and IRS can continue with the investigation using this information - and no warrants or probably causes ever required.
NSA analyst makes a "typo" and finds information on John Doe that, say, IRS wants. He then "mistakenly overshares" this information. Once it is detected, NSA instructs IRS to immediately forget the information, which they happily agree to do, though miraculously it turns out they've got exactly the same information by other, confidential, channel. Thus, no abuse of NSA facility ever happened, and IRS can continue with the investigation using this information - and no warrants or probably causes ever required.