Senator Carl Levin. (Yuri Gripas / Courtesy Reuters)

Earlier this month, with his piece "The NDAA Makes It Harder to Fight Terrorism," Brian Michael Jenkins added to the confusion surrounding the military detention provisions in the National Defense Authorization Act by promulgating the unfounded allegation that the NDAA exposes American citizens to arbitrary arrest and indefinite detention.

The new law does no such thing.

At its core, the NDAA reaffirms already existing U.S. law on the military detention of individuals captured in the country's fight against al Qaeda. Jenkins writes, "A fair way to assess this bill would be to ask, had this law been in effect since 2001, what would it have achieved?" His answer: some 20 "jihadist terrorists," including U.S. citizens and lawful resident aliens, who are today in civilian custody would instead "be in military custody."

The problem with Jenkins' hypothetical is that U.S. citizens and lawful resident aliens are expressly excluded from section 1022 of the NDAA. The law applies only to a narrow category of foreign al Qaeda members who participate in planning or conducting attacks against the United States and are "captured in the course of hostilities." And although section 1021 of the statute does not exclude U.S. citizens, this provision does not change existing military detention authority. The law specifically states: "Nothing in this section shall be construed to affect existing law or authorities relating to the detention of United States citizens, lawful resident aliens of the United States, or any other persons who are captured or arrested in the United States." In sum, neither section would have changed the outcome of any of the cases Jenkins wants to suppose.

The issue of indefinite detention arises from the capture of an enemy combatant in a war. According to the law of war, which, in the United States, dates back to the American Revolution, an enemy combatant may be held until hostilities come to an end. (See the 2004 case Hamdi v. Rumsfeld.) That did not change with the enactment of the Authorization for Use of Military Force in 2001, which authorized military operations against al Qaeda, the Taliban, and associated forces, and it did not change with the enactment of the NDAA.

Unfortunately, Jenkins is not the only one making this error. Activists on both the right and the left have alleged that the NDAA contains new authority for the military to detain American citizens. But the provision at issue repeats, word for word, the language that the Obama administration started using in federal court in March 2009 to delineate existing detention authority.

In fact, the White House's official statement on the NDAA -- released long before Obama decided to sign the bill -- expressly acknowledged that "the authorities codified in this section already exist." As if this were not enough, Senator Dianne Feinstein (D-Calif.) and I added an amendment on the Senate floor, which specifically states that the provision does not change "existing law or authorities relating to the detention of United States citizens, lawful resident aliens of the United States, or any other persons who are captured or arrested in the United States."

The Senate rejected a different amendment, offered by Feinstein, to exclude U.S. citizens from military detention. To the extent that such detention was authorized before the bill was enacted, it remains permissible today. However, that is very different from creating new or expanded authority for such detention. As Feinstein explained when the final bill was approved by the Senate, "[W]e have agreed to preserve current law for the three groups specified, as interpreted by our federal courts, and to leave to the courts the difficult questions of who may be detained by the military, for how long, and under what circumstances."

Prior to the NDAA, existing law authorized the military detention of U.S. citizens, at least in some cases. In 2004, the Supreme Court held, in Hamdi v. Rumsfeld, that "There is no bar to this nation's holding one of its own citizens as an enemy combatant." The defendant in the Hamdi case was a U.S. citizen captured on the battlefield in Afghanistan after taking an active part in hostilities against the United States. I believe that the Supreme Court's rationale in that case would apply to a U.S. citizen who joined al Qaeda and participated in an attack against the United States, whether the attack took place inside or outside the United States. Whether I am right or not, the existing authority was not changed in any way by the enactment of the NDAA.

The military did not engage in the arrest or apprehension of American citizens inside the United States before the enactment of the new law, and the new law does not authorize them to do so after. The posse comitatus law and associated policies precluding our military from engaging in law enforcement activities inside the United States remain in force, unchanged, as they should.

If an occasion did arise in which executive branch officials believed that a U.S. citizen had joined in an enemy attack against this country and should be held in military custody, the detainee would have access to legal counsel and could challenge the lawfulness of the custody in federal court pursuant to a writ of habeas corpus. Such an individual could not be held until the end of hostilities on the basis of a "suspicion" or "allegation," as some have argued -- but only if the government could prove on a habeas corpus challenge that the detainee had participated in hostilities against the United States and that the detention was constitutional.

The bottom line is that the NDAA puts Congress on record in support of existing military detention authority for individuals captured in the fight against al Qaeda, as set forth by the Obama administration and upheld by the federal courts, giving added legitimacy to ongoing military operations and preventing future administrations from adopting more expansive and problematic interpretations of military detention authority. That strengthens the fight against terrorism and makes the United States safer.