[pyre]

The US doesn't need a 'secret warrant' to ask for information from another country. They don't really need a warrant at all. They just ask for it. IIRC, even the NSA isn't legally bound to avoid spying on American citizens when they are out of the country.

[mpyne]

To avoid it, no. But if they do uncover evidence on American citizens it could not be used in a trial and must be filtered out (although, see 'parallel construction').