Well I am pleased that the DC Circuit did not find a way to screw this one up. In a nutshell this is what the decision means: You can't use a 2006 law to make conduct that occurred back in 2001 criminal-UNLESS it was already a crime back then. (duh)
Material support for terrorism was not a war crime in 2001- and it still isn't.
here is the decision...
Emptywheel has more here.