With his usual precision, my colleague Bob Levy, in his latest NSA post, has zeroed in on the basic question I put to him: “How can Congress, by mere statute, restrict an inherent power of a co-equal branch of government?” He grants that the president has inherent powers; but so does Congress, he adds, and if Congress expressly restricts the president’s powers, as with FISA, that “is persuasive when deciding whether the president has overreached.”

Not so fast. The problem with that is that the branches are then no longer “co-equal.” Rather, Congress is supreme, the president its mere agent—precisely the point I made in our recent debate when I spoke of Congress’s post-Vietnam rewrite of the Constitution in foreign affairs, much as the New Deal Congress did with domestic arrangements.

Bob points more precisely, however, to the Necessary and Proper Clause as the source of Congress’s power over the president. But that clause—to reduce a very complex issue to its essence—was written, in the context of the Articles of Confederation, to enable Congress to give effect to its and the other branches’ enumerated powers. As Chief Justice Marshall said in McCulloch v. Maryland (1819), the clause authorizes means that are “really calculated to effect any of the objects entrusted to the government,” like surveillance for national security purposes. When that power is used “improperly” to restrict the inherent power of another branch, serious separation-of-powers issues arise.

Congress does have a power to accomplish that end, however: It’s the power of the purse. It can simply cut off funds for projects—yet even here there are separation-of-powers questions that courts have never resolved. Given that the public seems to support the NSA program by 2 to 1, however, Congress is not likely to do that. This leaves us with Fourth Amendment issues, and as I said last time, that’s the business of the courts.

Two quick final points on Bob’s most recent post: First, the “parade of horribles” he presents—detention, tribunals, etc.—raises complex treaty and international law issues that are quite different, requiring separate analysis. Second, the animating sentiment at the time of the founding may have been fear of executive power—return of the king. By the time of the framing, however, after 11 years of experience with self-government, the Framers had a far more subtle understanding. As Madison put it in the Virginia ratifying convention, “The sword is in the hands of the British King. The purse is in the hands of the Parliament. It is so in America, as far as any analogy can exist.”