Lakin is on trial and U.S. Army must prove he is guilty beyond a reasonable doubt. If they cannot do so, it has no legal effect on whether Obama is the legitimate PResident even if it would make for very interesting commentary by the news media and congress members.
Right. But remember, in a military court of law, the orders are presumptively legal. The burden of proof with respect to the lawfulness of his orders, falls to the defendant see: United States v. Smith, 21 U.S.C.M.A. 231, 45 C.M.R. 5 (1972).
Moreover, the lawfulness of the order is a matter of law to be decided by the military judge, not the jury panel. The judge will instruct the jury panel that the orders were indeed lawful, and they will never hear Barack Obama's name mentioned, and certainly there will be no mention of his alleged ineligibility to hold office.
The prosecution will establish that Lakin missed movement by entering into evidence his deployment orders as well as testimony from superior officers that Lakin didn't deploy. That's the ballgame.