Let's be clear: WikiLeaks is not a news organization; it is a criminal enterprise. Its reason for existence is to obtain classified national security information and disseminate it as widely as possible--including to the United States' enemies. These actions are likely a violation of the Espionage Act, and they arguably constitute material support for terrorism. The Web site must be shut down and prevented from releasing more documents--and its leadership brought to justice. WikiLeaks' founder, Julian Assange, proudly claims to have exposed more classified information than all the rest of the world press combined. He recently told the New Yorker he understands that innocent people may be hurt by his disclosures ("collateral damage" he called them) and that WikiLeaks might get "blood on our hands."

With his unprecedented release of more than 76,000 secret documents last week, he may have achieved this. The Post found that the documents exposed at least one U.S. intelligence operative and identified about 100 Afghan informants--often including the names of their villages and family members. A Taliban spokesman said the group is scouring the WikiLeaks Web site for information to find and "punish" these informers.

Beyond getting people killed, WikiLeaks' actions make it less likely that Afghans and foreign intelligence services (whose reports WikiLeaks also exposed) will cooperate with the United States in the future. And, as former CIA director Mike Hayden has pointed out, the disclosures are a gift to adversary intelligence services, and they will place a chill on intelligence sharing within the United States government. The harm to our national security is immeasurable and irreparable.

And WikiLeaks is preparing to do more damage. Assange claims to be in possession of 15,000 even more sensitive documents, which he is reportedly preparing to release. On Sunday, Defense Secretary Robert M. Gates told ABC News that Assange had a "moral culpability" for the harm he has caused. Well, the Obama administration has a moral responsibility to stop him from wreaking even more damage.

Assange is a non-U.S. citizen operating outside the territory of the United States. This means the government has a wide range of options for dealing with him. It can employ not only law enforcement but also intelligence and military assets to bring Assange to justice and put his criminal syndicate out of business.

The first step is for the Justice Department to indict Assange. Such an indictment could be sealed to prevent him from knowing that the United States is seeking his arrest. The United States should then work with its international law enforcement partners to apprehend and extradite him.

Assange seems to believe, incorrectly, that he is immune to arrest so long as he stays outside the United States. He leads a nomadic existence, operating in countries such as Sweden, Belgium and Iceland, where he believes he enjoys the protection of "beneficial laws." (He recently worked with the Icelandic parliament to pass legislation effectively making the country a haven for WikiLeaks). The United States should make clear that it will not tolerate any country--and particularly NATO allies such as Belgium and Iceland--providing safe haven for criminals who put the lives of NATO forces at risk.

With appropriate diplomatic pressure, these governments may cooperate in bringing Assange to justice. But if they refuse, the United States can arrest Assange on their territory without their knowledge or approval. In 1989, the Justice Department's Office of Legal Counsel issued a memorandum entitled "Authority of the Federal Bureau of Investigation to Override International Law in Extraterritorial Law Enforcement Activities."

This memorandum declares that "the FBI may use its statutory authority to investigate and arrest individuals for violating United States law, even if the FBI's actions contravene customary international law" and that an "arrest that is inconsistent with international or foreign law does not violate the Fourth Amendment." In other words, we do not need permission to apprehend Assange or his co-conspirators anywhere in the world.

Arresting Assange would be a major blow to his organization. But taking him off the streets is not enough; we must also recover the documents he unlawfully possesses and disable the system he has built to illegally disseminate classified information.

This should be done, ideally, through international law enforcement cooperation. But if such cooperation is not forthcoming, the United States can and should act alone. Assange recently boasted that he has created "an uncensorable system for untraceable mass document leaking." I am sure this elicited guffaws at the National Security Agency. The United States has the capability and the authority to monitor his communications and disrupt his operations.

Last year, the Obama administration stood up a new U.S. Cyber Command (USCYBERCOM) to "conduct full-spectrum military cyberspace operations" in defense of U.S. national security. With the stroke of his pen, the president can authorize USCYBERCOM to protect American and allied forces by eliminating WikiLeaks' ability to disseminate classified information that puts their lives at risk.

WikiLeaks represents a clear and present danger to the national security of the United States. If left unmolested, Assange will become even bolder and inspire others to imitate his example. His group is at this moment preparing to release tens of thousands of documents that will put the lives of our troops and our allies at risk. Will President Obama stop WikiLeaks from doing so--or sit back and do nothing?

Marc A. Thiessen is a visiting fellow at AEI.

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