Adam Yahiye Gadahn (born in California, converted to Islam, joined al Qaeda, has appeared in numerous al Qaeda videos) was charged in absentia with treason in 2006. He was the first to be charged with treason since 1952.
Treason is a very difficult charge to try, as it requires the testimony of two eyewitnesses. Since Carter met in secret with Hamas (and, obviously, members of Hamas would be unlikely to cooperate with a treason trial), it would be almost impossible to prove a treason charge in this case (even though we all know that what he did was treasonous).
system that we have is proven innocent,until proven guilty.
at times though to except.
so i say pox on the bastard.