I don't believe the AUMF argument was weak. And I do think it was necessary in order to assert long-held principles.
If congress authorises the president to take ALL steps necessary to prosecute a war, the President should be able to take that to include spying on americans who might be communicating with the enemy. That is certainly a step to prosecute the war.
TO the degree that was a necessary step, congress could easily enumerate the things it is NOT allowing the president to do, or could enumerate the powers it is giving the president. It probably wouldn't pass constitutional muster for the reasons given above, but the courts hate to restrict things when congress didn't bother to do so.
I disagree with your point, for numerous reasons. But you are certainly entitled to keep your position on this, and you have well laid out why you hold the way you do.
I'm not going to flesh out my rationale here, but will give bullet points.
Whenever, during the present war, the President shall deem . . . public safety demands it, he may cause to be censored under such rules and regulations as he may, from time to time establish, communications by mail, cable, radio, or other means of transmission passing between the United States and any foreign country.
If (I think it's a matter of "when") the DoJ drops the AUMF argument, will you think it was a weak argument, or a strong argument?
I just bumped into an earlier post of mine on the same subject ...
http://www.freerepublic.com/focus/f-news/1573554/posts?page=95#95