When WikiLeaks founder Julian Assange released his latest document trove—more than 250,000 secret State Department cables—he intentionally harmed the U.S. government. The release of these documents damages our national interests and puts innocent lives at risk. He should be vigorously prosecuted for espionage.

The law Mr. Assange continues to violate is the Espionage Act of 1917. That law makes it a felony for an unauthorized person to possess or transmit "information relating to the national defense which information the...