What Exactly is Unclear About “Expressly” and “Shall Not”?

Adam Serwer has a helluva strange piece up today about Dianne Feinstein’s recently passed amendment blocking indefinite detention of US citizens and legal residents captured on US soil. Here’s the nut of the thing:

The question of what the Senate actually did hinges on language in the amendment that reads: “An authorization to use military force, a declaration of war, or any similar authority shall not authorize the detention without charge or trial of a citizen or lawful permanent resident of the United States apprehended in the United States unless an Act of Congress expressly authorizes such detention” (emphasis mine). It’s that “unless” that the supporters of indefinite detention latched onto.

“Senator Feinstein’s amendment…does not prohibit military detention if it is expressly authorized by law,” said Levin, “which I read as a statute authorizing the use of military force itself or some other act of Congress.”….But Feinstein said that the Levin interpretation was incorrect, and that based on a federal court decision in the case of Jose Padilla (the only American accused of terrorism to be held in military detention in the US) the 2001 AUMF doesn’t count as an authorization to detain US citizens captured on American soil indefinitely. 

This is just….weird. I can imagine thinking that an authorization of military force could also be interpreted as an authorization for indefinite detention, except for the fact that Feinstein’s amendment explicitly says that an authorization of military force “shall not” be interpreted that way. Only an act of Congress that “expressly” authorizes indefinite detention may be interpreted to allow indefinite detention.

On a related note, why is Feinstein relying on the Padilla case for backup? That was a pretty fuzzy opinion, wasn’t it? Isn’t Hamdi more on point? And who cares anyway? Feinstein’s amendment would supersede any court ruling based on statutory grounds, and wouldn’t matter if the Supreme Court ever ruled that indefinite detention was OK on constitutional grounds. What am I missing here?