Contrary to the claims of some politicians and others who should know better, Edward Snowden did not commit treason. Treason is a specific crime defined in the Constitution, and it is particularly difficult to prosecute. As Seth Lipsky wrote in the WSJ this week:

[T]reason turns out to be unique in American law. It is the only crime that the Constitution forbids Congress from defining. It is the only crime to which a court may never accept a confession given to the police. It is the only crime for which restrictions are laid down on how much evidence juries must hear. The Constitution itself underscores that the Founders feared treason law. . . .

“Treason against the United States,” the Constitution says, “shall consist only in levying War against them, or in adhering to their Enemies, giving them Aid and Comfort.” It adds: “No Person shall be convicted of Treason unless on the Testimony of two Witnesses to the same overt Act, or on Confession in open Court.”

What this adds up to is that a person has to do one of two things to be a traitor: either levy war or adhere to (form an attachment to, the Supreme Court once said) our enemies, giving them not only aid but also comfort. The two-witness rule has also made treason cases rare in American history.