The Canon of Constitutional Avoidance:
In the hearings earlier today, Attorney General Gonzales argued that FISA's exceptions should be read broadly under the canon of construction of avoiding constitutional doubt. Consider this exchange between Gonzales and Senator Feinstein:
FEINSTEIN: What in FISA specifically, then, allows you to conduct electronic surveillance within America, on Americans?

GONZALES: I believe that it's Section 109, which talks about persons not engaged in electronic surveillance under cover of law except as authorized by statute. And I may not have it exactly right.

We believe that that is the provision in the statute which allows us to rely upon the authorization to use military force.

Now, you may say, "Well, that — I disagree with that construction." That may be so. There may be other constructions that may be fairly possible. We believe this is a fairly possible reading of FISA. And as the Supreme Court has said under the canon of constitutional avoidance, if you have two possible constructions of a statute and one would result in raising a constitutional issue, if the other interpretation is one that is fairly possible, that is the interpretation that must be applied.

And if you reject our interpretation of FISA, Senator, then you have a situation where you've got an act of Congress intention with the president's constitutional authority as commander in chief. And the Supreme Court has said when that happens you go with another interpretation if it's a fair application. And that's what we've done here.
  One difficulty with Gonzalez's argument, it seems to me, is that the Supreme Court didn't rely on this argument when DOJ tried it before. Specifically, DOJ made a similar argument in its brief filed in Hamdi v. Rumsfeld, but found no takers among the Justices.

  In Hamdi, the Supreme Court confronted a question similar to the one raised by FISA and the NSA program. Yaser Hamdi was being held as an enemy combatant, and claimed that his detention violated 18 U.S.C. 4001(a): "No citizen shall be imprisoned or otherwise detained by the United States except pursuant to an Act of Congress." The question was whether the AUMF was an Act of Congress that authorized Hamdi's detention, such that the detention did not violate Section 4001.

  DOJ's brief relied in part on the canon of constitutional avoidance. It argued that Section 4001 should be construed to avoid a clash with Article II Commander in Chief powers:
The canon of constitutional avoidance counsels against interpreting Section 4001(a) in a manner that would interfere with the well-established authority of the Commander in Chief to detain enemy combatants in wartime. See Public Citizen v. United States Dep’t of Justice, 491 U.S. 440, 466 (1989).
  Justice O'Connor's plurality opinion and Thomas's dissent created fives votes for the view that the AUMF did in fact satisfy the statute, so the detention was lawful. However, none of the opinions filed in that case relied on the canon of constitutional avoidance to construe 18 U.S.C. 4001. Scalia's dissent mentioned the canon, but rejected its application in the Hamdi case: "I do not think this statute even authorizes detention of a citizen with the clarity necessary to satisfy the interpretive canon that statutes should be construed so as to avoid grave constitutional concerns." The rest of the opinions didn't mention it.

  Given that none of the Justices accepted DOJ's invitation to apply the canon of constitutional avoidance in Hamdi, it's not obvious to me why a court would think the canon applies in somewhat analogous circumstances to interpret FISA.