In a significant ruling today, a federal appeals court overturned a conviction of Salim Hamdan, Osama bin Laden’s driver, obtained through a military commission. Judge Brett Kavanaugh, a George W. Bush appointee seen as a possible conservative Supreme Court justice, wrote in a ruling for a three-judge panel of the DC Circuit Court that Hamdan could not be convicted under a military commission for “material support” for terrorist organizations before 2006, when the military commission process was inaugurated.

Hamdan, who spend several years in Guantanamo, has since been released to Yemen. And all others convicted in a military commission under the material support statute have either been returned to their home countries, or were convicted on multiple counts beyond just material support. However, this has the potential of narrowing the military commission process used by both the Obama and Bush Administrations, and making it harder for them to convict on this tangential relationship to terrorism.

The judges ruled that material support of terrorism, a common terrorism-related charge in U.S. civilian criminal courts, is not a war crime under international law and therefore is beyond the scope of what military commissions were permitted to do as originally constituted.

“When Hamdan committed the conduct in question, the international law of war proscribed a variety of war crimes, including forms of terrorism. At that time, however, the international law of war did not proscribe material support for terrorism as a war crime. Indeed, the Executive Branch acknowledges that the international law of war did not – and still does not – identify material support for terrorism as a war crime. Therefore, the relevant statute at the time of Hamdan’s conduct….did not proscribe material support for terrorism as a war crime,” Judge Brett Kavanuagh wrote.

Kavanaugh did not go so far to say that the ruling would compel Hamdan’s release; he still believes that Hamdan could be held under the law of war, a prelude to an indefinite detention. He also claimed that post-2006 material support would be punishable through a military commission (I believe Hamdan was in custody at Guantanamo by that time).

This just reveals the clumsiness of the military commission process. Material support is a viable charge in an Article III court, but Republicans won’t allow terror suspects to face charges in civilian courts anymore. So you have this alternate process, which is much harder to use without evidence of established war crimes. As Adam Serwer writes, the military loved to use the material support statute:

“This is a massive blow to the legitimacy of the military commissions system,” says Zachary Katznelson, a senior attorney at the ACLU. The commissions “have been trying people for years for something that isn’t even a war crime.”

War crime or not, prosecutors love material support charges because they’re vague and relatively easy to prove. Material support often involves conduct that might not necessarily be violent—like driving bin Laden’s car or cooking his food—that somehow helps a terrorist group.

It’s not just a few Gitmo detainees who have faced these charges. Every single detainee at Gitmo who has been convicted by military commission has been at some point charged with material support for terrorism. Now a federal judge—one appointed by Bush!—says that’s all bogus. And it’s not just material support charges that could be affected. Conspiracy charges, which were also not a war crime under United States law before 2006, could be thrown out for similar reasons.

The Justice Department could appeal to an en banc panel or the US Supreme Court. Since this ruling undermines the use of military commissions, I suspect they will. Or, they could merely decline to use military commissions very much, and just warehouse prisoners under “enemy combatant” rules, indefinitely. The legal black hole at Guantanamo just grew larger today, but that doesn’t mean it will ever get so big that it cannot be ignored. Don’t expect this to come up at tonight’s debate, for example.