If he's not a citizen, then this isn't his country.
That's OK, the Constitutional definition of treason is different than the dictionary one.
The Constition says:
Treason against the United States shall consist only in levying War against them, or in adhering to their Enemies, giving them Aid and Comfort.
Indeed. A traitor is subject to a trial and upon conviction, a hanging.
Non-uniformed enemy combatants (spies and saboteurs) can be shot on sight.
Not that I'm advocating that, and indeed, it would be a VERY BAD THING to make him a martyr in the left's eyes.
It's just the legal reality.
Although I am as certain as I can be that he is not a Natural Born Citizen, I think he might actually be a citizen and therefore rates a fair and open trial.