A blow for the White House spying program

The administration has insisted that the president has the power to spy on American citizens without warrants pursuant to his authority as commander in chief, and that Congress somehow implicitly gave him that power when it authorized the use of force against those who attacked the United States on 9/11. But if the administration really thought that it had the authority to monitor the calls of both foreigners and U.S. citizens without getting warrants at all, how could it possibly have also thought that a measure that would have authorized something less -- spying only on foreigners, and even then with warrants approved by a court -- would be constitutionally suspect?