First, from Daniel J. Solove, an item called "Hypothetical: What If President Bush Were Correct About His Surveillance Powers? Here's most of Solove's post:
Suppose the President is right that he has the power to do this based on his "inherent authority" as Commander-in-Chief. The implications are quite alarming. It means that the President, in his sole discretion, can secretly authorize the NSA to engage in electronic surveillance on U.S. citizens until the War on Terrorism is over. This is a war without a foreseeable end. Under his argument, there seems to be no reason why he can't authorize other agencies to engage in surveillance, such as the FBI and CIA. And why does it need to be limited just to wiretaps? Perhaps video surveillance, bugs, searches of homes, gathering documents, and more.
Under his argument, Bush could continue to ignore the requirements of any law that stands in his way. What could Congress do? Congress could try to enact a law to clarify that it wants the President to abide by existing laws. Of course, the President could veto that law, but suppose Congress overrode the veto. According to the President's logic, he could still say that his "inherent authority" allows him to ignore it.
The problem with Bush's argument is that he has articulated virtually no conceivable limits to his power. The stakes of the debate aren't just about what the President has already done. They are about what the President has defiantly declared he has the power to do in the future.
Bruce Schneier has written a long, thoughtful piece on this issue. He shows, among other things, that our government's recent justifications for unwarranted wire-tapping ignore the fact that such acts were judged illegal in 1970 proceedings. I recommend his entire article, titled, appropriately, The Security Threat of Unchecked Presidential Power. Along the way he says:
This is indefinite dictatorial power. And I don't use that term lightly; the very definition of a dictatorship is a system that puts a ruler above the law. In the weeks after 9/11, while America and the world were grieving, Bush built a legal rationale for a dictatorship. Then he immediately started using it to avoid the law.
This is, fundamentally, why this issue crossed political lines in Congress. If the president can ignore laws regulating surveillance and wiretapping, why is Congress bothering to debate reauthorizing certain provisions of the Patriot Act? Any debate over laws is predicated on the belief that the executive branch will follow the law.
UPDATE: And perhaps he also lied to us. It's been pointed out that President Bush used to assure us not to be afraid of the power of the Patriot Act:
In 2004 and 2005, Bush repeatedly argued that the controversial Patriot Act package of anti-terrorism laws safeguards civil liberties because US authorities still need a warrant to tap telephones in the United States.
Read more about it here at the AFP.