The report on Fox News that Sergeant Bergdahl at one point during his captivity declared himself a “mujahid,” or warrior for Islam, and may even have been allowed to carry a weapon puts at a premium an understanding of treason. Sergeant Bergdahl hasn’t been accused of treason and would be considered innocent until proven otherwise. The burden is always and only on the accusers. But all the more reason to understand what treason is and why it is so special under American law.

Treason is the only crime the Constitution pre-empts Congress from defining. It’s also the only crime to which such authorities as the police and the FBI mayn’t take a confession. It is the only crime of which the judicial branch is barred from convicting someone through the normal rules of due process. Treason is special, made so because of abuse by the English kings. And it has often been tested in our courts in ways that guide our thinking in the current crisis.

Treason against the United States, our Constitution says, may consist only in levying war against them or adhering to their enemies, giving them aid and comfort. Feature the liberality of that formulation. One can, even in war, dissent from our government without committing treason. The plain language suggests that one can even adhere to an enemy without committing treason. That is, an American whose family came over from, say, Germany, could have privately rooted for Germany in World War I.

So long as he didn’t do anything about it. But if one gives aid and comfort, then it’s treason. And whether or not one adheres to an enemy, one may never levy war against the United States. That is treason. We mark that not to accuse Sergeant Bergdahl but just to offer some context for the latest report. If it turns out that Sergeant Bergdahl was carrying a weapon against the United States, the story becomes a whole new ballgame.

Even then, there are hurdles, for the Constitution sets a high bar for a conviction of treason. “No Person shall be convicted of Treason,” it says, “unless on the Testimony of two Witnesses.” They have to witness an act. It has to be the same act. And it has to be overt. The only acceptable confession to treason is one made in court. And it can’t be a closed session of court. It has to be open court. All that’s in the Constitution.

The Supreme Court has taken great care with treason. Bollman and Swartwout, two confederates of Aaron Burr, were let off by Chief Justice Marshall because conspiring to levy war, which they’d done, and actually levying war, which hadn’t been done, are different things. The conviction of Tomoya Kawakita, who’d been born in America but was in Japan when World War II erupted and went to work in an arms plant, was sustained.

The plant used American POWs as labor. It seemed the courts were inclined to given Kawakita the benefit of the doubt but were horrified at evidence that he had struck American POWs. The Supreme Court sustained his conviction and his death sentence. President Eisenhower commuted it to life in prison; President Kennedy later pardoned him on the condition he be deported to Japan and banned from returning to American soil.

Just how tempting treason law is to abuse is illustrated in the case of Tokyo Rose — or the most famous of the several “Tokyo Roses,” Iva Ikuko Toguri D’Aquino. She had been born at America but was in Japan when war broke out. She refused to give up her American citizenship and ended up working at Radio Tokyo, where she was part of the notorious broadcast “Zero Hour,” which Allied POWs had been tortured into helping produce.

In Japan after the war, D’Aquino tried to claim $2,000 offered by Cosmopolitan Magazine and the International News Service for an interview with Tokyo Rose, according to the account of her case on Wikipedia. She was arrested but released. When she returned to America, columnist Walter Winchell went after her, and she was put in the dock and convicted of treason. She served six years. Then, in 1977, the Chicago Tribune took another look at her case and discovered that two witnesses had lied.

President Ford gave her a full pardon, and she later actually won a citizenship award for courage from the World War II Veterans Committee. Her case does not mean that treason is a figment. There is such a thing as treason, it is a heinous crime, and it needs always to be understood by those who take war seriously. But Tokyo Rose is a reminder that even with all the protections the Constitution puts up against abuse of treason, one needs to keep a level head.

Never more so, it seems to us, than when our government is in the process of ending a war without a complete victory. It’s a time to take the issues of desertion and possible treason seriously. George Washington once built a gallows 40 feet high to deal with deserters. Everyone is owed a full investigation. But it’s also a time to comprehend that the fog of war envelops not only the battlefield but also the political sphere. That is why the meaning of treason has been made so clear.