Gun...thanks for the link to the blog with that legal analysis. That is an excellent blog and I have it bookmarked as a favorite. It is always good to see all aspects of an argument.
While the court cases cited in your excerpt and in the complete blog article are interesting, those cases before 1978 are not controlling in this situation due to the change in Federal law, ie FISA. Further, Truong is not controlling (even according to the FISA Review Court in Sealed Case No. 02-001) because it is regarding wiretaps that took place before FISA was inacted. (Interestingly, your blogger uses both Truong and this case, but leaves out the part from the FISA Review Court opinion that says it is no longer relevent

) And again, Duggan does not question that the President
prior to FISA had unfettered power to wiretap in the interest of national security...but it does not indicate that it is unregulated after FISA.
You have to recall that FISA and Title III were created specifically because of this grey area conflict between US Constitution Article II and the 4th Amendment. Every president from FDR to Nixon had abused Article II in order to gather "political intelligence" by authorizing warrantless search/wiretaps on political enemies by identifying them as potential enemies of the US. And then there was J. Edgar Hoover and his internal investigations of citizens under the ruse of protecting national security. In the end this all came to light with the Church Commission and as a result Congress enacted FISA and modified Title III to regulate foreign and domestic intelligence gathering respectively.
FISA, Title III and the Electronic Commnunications Privacy Act--even after amendment by the Patriot Act--provide limits to when and how long the President/Attorney General can authorize warrantless wiretaps. IE, the President can authorize warrantless wiretaps under Article II, however Congress has limited that power. 50 U.S.C. § 1809(a)(1) specifically prohibits electronic surveillance except where granted by statute.
By statute, FISA grants the President the power of warrantless wiretaps for no more than one year IF the surveillance will not acquire communication where a US person is a party, 50 U.S.C. § 1802(a)(1) & (b) and restricts unlimited warrantless wiretaps in time of war to 15 days after the declaration by Congress, 50 U.S.C. § 1811.
Beyond that, the wiretap must have a warrant issued by the FISA Court within 72 hours of the start of the surveillance.
This program has been going on for years and directed at US persons according to the NYT.
There are a couple of things that really set off alarms about this case: 1) The acting Attorney General, James B. Comey, refused to re-approve the program while he was filling in for Ashcroft, who had been hospitalized. The program had to shut down because of his objections as to whether the President had legal authority to continue. Ashcroft had to give approval from his intensive care bed. 2) The NSA insiders who leaked the info would not have committed an act of treason (and yes, I do think what they did constitutes treason) without thinking that the program was seriously illegal...it had to go through their mind that leaking this could bring sever punishment and possibly even a death penalty. 3) A FISA judge quit in protest...yes, he may be a liberal, but he had been sitting on the FISA Court for all of Bush's administration and yet it took till now, over this issue, for him to resign. This is a person who above anyone should know how easy it would have been for the Administration to get a warrant, regardless of whether they thought they needed to or not.