Treason is an unusual crime in this country. It's elements are actually spelled out in the constitution (Article 3.) It is difficult to charge and even more difficult to prove. In fact the standard of proof is even higher than "beyond a reasonable doubt;" for example, circumstantial evidence is inadmissible in a trial for Treason. The difficulty of actually proving Treason is the reason most traitors are tried for other crimes; the Rosenbergs for example were not convicted of treason but rather espionage. Of the relatively small number of people charged with Treason since the founding of the Republic (less than 50 - nearly half of whom were charged in "The Whiskey Rebellion") a surprisingly high number were either acquitted, granted clemencies or had their convictions overturned on appeal.