So, in the interest of Doing My Part, I give you A Layman's Guide to Dealing With the Military Commissions Act of 2006, linked and under the cut. It's a flowchart detailing who the MCA applies to and what you can do if you find yourself charged under it. Note that I am absolutely not a lawyer -- not even a law student -- and this is merely a layman's reading. If you find yourself charged with terrorist activities or conspiracy to commit same, for God's sake, get a competent attorney.
But, with that said, please feel free to spread this image around; it's free under Creative Commons Attribution-Noncommercial-ShareAlike.
EDIT: I've seen a lot of arguments claiming that U.S. citizens can be tried under the MCA, and some people have taken me to task for supposedly neglecting this. They cite the first definition given in Sec. 948a:
(1) UNLAWFUL ENEMY COMBATANT- (A) The term `unlawful enemy combatant' means--and point out that "person" can apply to anyone, including citizens.
(i) a person who has engaged in hostilities or who has purposefully and materially supported hostilities against the United States or its co-belligerents who is not a lawful enemy combatant (including a person who is part of the Taliban, al Qaeda, or associated forces); or
(ii) a person who, before, on, or after the date of the enactment of the Military Commissions Act of 2006, has been determined to be an unlawful enemy combatant by a Combatant Status Review Tribunal or another competent tribunal established under the authority of the President or the Secretary of Defense.
However, that's a definitions section. "Alien" is defined two bullet-points down:
(3) ALIEN- The term `alien' means a person who is not a citizen of the United States.And, finally, Sec. 948c, "Persons subject to military commissions" consists wholly of the following statement:
Any alien unlawful enemy combatant is subject to trial by military commission under this chapter.So, no. Maybe you can be declared an unlawful enemy combatant, but as long as you're a U.S. citizen, you can't be declared an alien unlawful enemy combatant, and the MCA does not apply to you.
FWIW, the Cato Institute agrees with me.