Just heard at the Senate Judiciary Committee hearing today on FISA and the NSA program (close to verbatim):

Sen. Specter: Isn’t it true that an act of congress can neither expand not contract the president’s constitutional authority under Article II?

DOJ representative: Well, congress can reasonably regulate the president’s Article II powers …

I should note that testifying at a public hearing in court or congress is very difficult. Having been in the positions of both asking and answering questions at hearings, I can attest that it is much easier to ask them. The DOJ rep is doing a generally fine job and I think he was just being careful. Eventually, it became clear to him that Sen. Specter was being helpful to his position, and he gratefully agreed with Specter’s conclusion that if the president has constitutional authority (e.g., to order interception of the enemy’s international communications in wartime), congress cannot detract from that authority.