Rep. Peter King (R-N.Y.) sparked a firestorm last week with his suggestion that Glenn Greenwald, the Guardian reporter who exposed the National Security Agency’s terrorist surveillance activities, ought to be arrested before he can publish more U.S. secrets.

Greenwald responded that King wanted to prosecute him for “the crime of doing journalism.” Wrong. Greenwald’s crime is violating 18 USC § 798, which makes it a criminal act to publish classified information revealing government cryptography or communications intelligence.

The law is absolutely clear. It states: “Whoever knowingly and willfully communicates, furnishes, transmits, or otherwise makes available to an unauthorized person, or publishes , or uses in any manner prejudicial to the safety or interest of the United States or for the benefit of any foreign government to the detriment of the United States any classified information— (1) concerning the nature, preparation, or use of any code, cipher, or cryptographic system of the United States or any foreign government; or (2) concerning the design, construction, use, maintenance, or repair of any device, apparatus, or appliance used or prepared or planned for use by the United States or any foreign government for cryptographic or communication intelligence purposes; or (3) concerning the communication intelligence activities of the United States or any foreign government; or (4) obtained by the processes of communication intelligence from the communications of any foreign government, knowing the same to have been obtained by such processes— Shall be fined under this title or imprisoned not more than ten years, or both.”

Note that emphasis, which I added: The law specifically states that publishing, not just divulging, such information is a federal crime. Greenwald clearly violated this law (as did The Post, for that matter, when it published classified details of the NSA’s PRISM program).

As a matter of prosecutorial discretion, the Justice Department may choose not to charge The Post or Greenwald for these criminal acts. But it is neither outrageous nor incorrect for Peter King to state that they are criminal acts. Nor is it unreasonable for a federal lawmaker to argue that federal law should be enforced.

Leak defenders like to cite the Supreme Court’s 1971 decision in the Pentagon Papers case as protecting the right of journalists to publish classified information. This is incorrect. While the court rejected the government’s efforts to suppress publication of the Pentagon Papers, the court said the decision to go ahead with publication of the classified materials could still result in criminal prosecution. As Justice Byron White, joined by Justice Potter Stewart, wrote in their concurring opinion: “Section 798 … in precise language, proscribes knowing and willful publication of any classified information concerning the cryptographic systems or communication intelligence activities of the United States, as well as any information obtained from communication intelligence operations. If any of the material here at issue is of this nature, the newspapers are presumably now on full notice of the position of the United States, and must face the consequences if they publish. I would have no difficulty in sustaining convictions under these sections.”

King called for the application of this law in Greenwald’s case not just because he has already published classified signals intelligence but because Greenwald has publicly stated that he possesses more unpublished signals intelligence – and that he intends to publish theses U.S. secrets as well.

“We are going to have a lot more significant revelations that have not yet been heard over the next several weeks and months,” Greenwald told the Associated Press. “There are dozens of stories generated by the documents he [Edward Snowden] provided, and we intend to pursue every last one of them.”

In other words, not only has Greenwald committed a federal crime, he has also publicly announced his intent to commit further crimes that could cause enormous harm to our national security. King’s not unreasonable suggestion is that the U.S. government act to stop him.

Indeed, this week, the Guardian published yet another damaging report, exposing the signals intelligence activities of our ally, Britain and U.S. efforts to intercept the top-secret communications of former Russian president Dmitry Medvedev.

Many do not realize it, but the law is much stricter with the disclosure of signals intelligence than it is with the disclosure of other classified information. All leaks of classified information are damaging, but the exposure of signals intelligence can be catastrophic. Just think back to World War II. If someone had compromised a human intelligence source, a spy or double agent who had infiltrated the Nazi high command, that asset could lose his life, but we would have lost a relatively small amount of intelligence. But if someone had exposed the allies’ top secret ULTRA program — through which we broke the encrypted radio and telegraphic codes used by the Nazi leadership — it could very well have altered the outcome of the war.

Signals intelligence is of similar import in the war on terror. We cannot track small terrorist cells with spy satellites. The only way we can disrupt the terrorists’ plans is by getting them to tell us their plans. In the absence of interrogation, one of the only ways to do that is through signals intelligence.

That is why the NSA’s surveillance activities are so essential — and why Greenwald could face prosecution for exposing them.

Read more from Marc Thiessen’s archive, follow him on Twitter or subscribe to his updates on Facebook.