"OTOH, treason laws have nothing to do with Snowden; espionage laws might, but that's a different issue"

There's some overlap between the two although I don't mean it in a strict, technical sense so much as betraying his country to its enemies with criminal action. Espionage is spy activity, often moving information. His actions mostly fall into that. Treason concept often includes aiding and abeitting enemy military. A significant part of that today are the cyber commands on various sides. He certainly gave our enemies a heads up about what we were doing while giving us no such advantage on them. That can be construed as treason given what effect it would have if war broke out.

Note: Apparently didn't help North Korea any during Sony response. ;) So, effect on wartime capability is debatable. I'd say espionage charge for legal leaks at the least with a deal (maybe immunity) due to legit whistleblowing.