Here is another good article making the point that what President Bush did was totally legal.
Unwarranted complaints
http://www.iht.com/articles/2005/12/27/opinion/edcasey.php
Shortly after the Sept. 11 attacks, President George W. Bush ordered surveillance of international telephone communications by suspected members of Al Qaeda overseas, even if such calls also involved individuals within the United States. This program was adopted by direct presidential order and was subject to review every 45 days. Judicial warrants for this surveillance were neither sought nor obtained, although key members of Congress were evidently informed. The program's existence has now become public, and howls of outrage have ensued. But in fact, the only thing outrageous about this policy is the outrage itself.
The U.S. president has the constitutional authority to acquire foreign intelligence without a warrant or any other type of judicial blessing. The courts have acknowledged this authority, and numerous administrations, both Republican and Democrat, have espoused the same view. The purpose here is not to detect crime, or to build criminal prosecutions - areas where the Fourth Amendment's warrant requirements are applicable - but to identify and prevent armed attacks on American interests at home and abroad. The attempt, by Democrats and Republicans alike, to dismantle the president's core constitutional power in wartime is wrongheaded and should be vigorously resisted by the administration.
"Even if Congress had intended to restrict the president's ability to obtain intelligence in such circumstances, it could not have constitutionally done so. The Constitution designates the president as commander in chief, and Congress can no more direct his exercise of that authority than he can direct Congress in the execution of its constitutional duties. As the FISA court itself noted in 2002, the president has "inherent constitutional authority to conduct warrantless foreign intelligence surveillance."
That's exactly right. Al Qaida cells inside the U.S. are a military incursion onto our soil. Their communications back to their overseas headquarters are fair game. It's really no different than if WWII German commandos had come ashore, and were calling back to Berlin. Enemy troops on our soil (as defined by those who contact and coordinate with enemy units abroad) are a military threat, and should be dealt with accordingly.