In the aftermath of the New York Times's illegal disclosure of surveillance by the National Security Agency, the Senate now debates whether to amend the Foreign Intelligence Surveillance Act (FISA), the law that formulates a procedure for the president to obtain warrants to wiretap foreign individuals and entities within the United States. The senators claim they are considering such legislation not to bury the NSA program, but to save it. It's time for a legal primer on the Constitution and national security law.

In Article II, the Constitution establishes the president as commander in chief. As such he has inherent authority to conduct warrantless surveillance for the purpose of acquiring foreign intelligence information. He does not have the authority to close banks, seize steel mills, or raise our taxes; he does have it to get battlefield information about an enemy who has killed thousands of us on our soil and threatens to do so again.

No court opinion denies this constitutional authority to the president. All federal appellate courts that have considered the issue, including the FISA appeals court, have recognized such authority. The Supreme Court, over three decades ago, emphatically specified in the Keith case that it would leave this issue to another day. In doing so, the Court provided a clear indication that foreign surveillance is not domestic surveillance.

The Keith Court held that the president does not have authority to conduct warrantless searches of entities that are "domestic," i.e., where "[t]here is no evidence of any involvement, directly or indirectly of a foreign power." This decision, the Court stressed, makes "no judgment on the scope of the president's surveillance power with respect to the activities of foreign powers, within or without this country." (Emphasis added.) Keith made clear that "domestic" wiretapping is a legal term of art that does not turn on whether the surveillance takes place in the United States. Media misuse of that term to characterize the NSA surveillance, where one party is foreign and linked to al Qaeda, indicates an absence of legal sophistication or an attempt to prejudice the issue, or both.

Post-Keith appellate decisions, before and after the 1978 FISA statute, uphold the president's inherent constitutional authority for warrantless acquisition of foreign intelligence information.

In 1973, the U.S. Circuit Court of Appeals for the Fifth Circuit relied on one of its previous decisions in holding that it "reaffirms . . . the President may constitutionally authorize warrantless wiretaps for the purpose of gathering foreign intelligence." The court cited a Federalist Papers theme as "buttress[ing]" its decision: "the President must take great care to safeguard the nation from possible foreign encroachment."

In 1974, the majority of the entire Third Circuit (sitting en banc) considered a challenge to an espionage conviction where warrantless surveillance had not only been carried out by the president but also used at trial. In affirming the conviction, the court stated, "The importance of the President's responsibilities in the foreign affairs field requires the judicial branch to act with the utmost care when asked to place limitations on the President's powers in that area. As Commander-in-Chief, the President must guard the country from foreign aggression, sabotage, and espionage."

Significantly in this case, there was a statute (not FISA) prohibiting anyone, including government personnel, from monitoring communications. The court noted that Congress had given "little or no discussion" of whether the statute had any bearing on the "President's constitutional duties as Commander-in-Chief and as administrator of the nation's foreign affairs." Had Congress done so, it "would have recognized," said the Court, "that any action by it that arguably would hamper . . . the President's effective performance of his duties in the foreign affairs field would have raised constitutional questions."

In 1980, the Fourth Circuit considered the issue of warrantless surveillance after FISA was passed. However, because the wiretapping had taken place prior to FISA's enactment, the government had to rely on the constitutional basis to uphold the warrantless surveillance. The Carter Justice Department argued that it did not seek a warrant in the spy investigation because there is a "foreign intelligence" exception to the Fourth Amendment warrant requirement. In fact, Carter's legal shop claimed this exception applied if the surveillance "is to any degree directed at gathering foreign intelligence." (Emphasis added.) Perhaps the former president forgot his prior legal position when he decried warrantless searches at Coretta Scott King's funeral. Although the Court rejected Carter's expansive definition of foreign intelligence, it upheld the national security exception to the warrant requirement.

The Fourth Circuit explained that a warrant in the area of foreign intelligence would "add a procedural hurdle" that could increase the "chance of leaks" and "delay executive response to foreign intelligence threats." Such threats "require the utmost stealth, speed, and secrecy."

Although it did not have to do so to reach its decision, the Fourth Circuit discussed FISA, stating it requires, "prior judicial approval for some foreign intelligence surveillance." The act, though, "does not . . . transport" the warrant requirement "unaltered into the foreign intelligence field." Thus, after passage of FISA, this court took great pains to stress that a FISA warrant is not the only legal method for the president to obtain foreign intelligence.

Most significantly, in 2002, the FISA appellate court cited the Fourth Circuit case saying, "The Truong court, as did all other courts to have decided the issue, held that the President did have inherent authority to conduct warrantless searches to obtain foreign intelligence information. . . . We take for granted that the President does have that authority and, assuming that is so, FISA could not encroach on the President's constitutional power."

So there is the rub. Under established case law, parts of FISA are unconstitutional in so far as they prohibit or limit the president's constitutional authority to collect foreign intelligence information.

There is an important rule of judicial review. Courts do not like to declare laws unconstitutional and will attempt to find language that "saves" them. That rule brings us to the president's arguing that the congressional resolution giving the president the Authority to Use Military Force (AUMF) permits him to wiretap consistent with FISA. In an irony too scrumptious to resist pointing out to the critics, the president's argument is an attempt to save FISA from being declared unconstitutional.

A little statutory history is required to understand this legal argument. When Congress passed FISA it contained two contradictory statements: (1) FISA and the criminal wiretap statute were the "exclusive means" by which there could be interception of wire and oral communications, and (2) a person is guilty of a crime if he intentionally "under color of law" (which is how the president does it) obtains foreign intelligence information, unless he is "authorized by statute." Like it or not, that's how laws get passed. Each side gets something. Those against any wiretapping got the gift of limiting the conduct to those two laws; proponents got the gift of an exception to that limitation: some other law.

There has been ill-informed criticism of the president's use of the broad language of the Authorization to Use Military Force ("use all necessary and appropriate force against" those responsible for 9/11) to support the argument that Congress passed a law that fits that FISA exception. For example, George Will groused recently in the Washington Post that the administration "incoherently argue[s] that the AUMF . . . authorized the NSA surveillance." Yet in the 2004 Hamdi case, a majority of the Supreme Court agreed with the president's argument.

Hamdi was an American citizen captured on the battlefield in Afghanistan and detained in the United States as an enemy combatant, meaning he was imprisoned but not charged with a crime. Hamdi argued he should be freed because there is a law mandating that "no citizen" shall be imprisoned unless there is an Act of Congress. There is no such act, claimed Hamdi. But five of the Supreme Court justices agreed that the AUMF could have such a broad reading. "[I]t is of no moment that the AUMF does not use specific language of detention. Because detention to prevent a combatant's return to the battlefield is a fundamental incident of waging war," the words "necessary and appropriate force" were a clear congressional authorization to detain Hamdi, according to Justice O'Connor's rather coherent opinion. No one can seriously argue that obtaining foreign intelligence information about the enemy is not a "fundamental incident of waging war."

An amendment to FISA would be nice as a political matter--the two branches in agreement and all those warm good feelings. But it is not necessary legally for the constitutional health of the NSA program.

Victoria Toensing, a founding partner of diGenova & Toensing, is a former Justice Department official and chief counsel for the Senate Intelligence Committee.