Most people tried for espionage in the US in the last two decades were not spies at all. The people who should have been tried and executed, for participating in torture, and for destroying evidence that could have led to convictions for torture, are still in charge.

Probably the overwhelming majority of actual spies in the US are not caught, because hardly anybody is even looking. And, the stuff they spy out is in the end mostly inconsequential, except insofar as it causes trouble for other spies.