He could have gone to Congress.
What does "gone to Congress" mean? You mean like just walking in the front door and demanding speaking time during a joint session of both houses? (not gonna happen) Or do you mean he could have contacted a congressman, which would give him a fairly high chance of being arrested within hours for being a traitor? (or do you think contacting a congressman with information about the NSA's activities would somehow remain quiet for long?)
Maybe you aren't aware of it, but under the US Constitution the Congress has special powers that are quite useful in situations like this.
Maybe you aren't aware of it, but the US Constitution doesn't seem to have much applicability to NSA activities.
He stole ~ 1.7 million highly classified intelligence documents, fled the country, and started leaking them to whomever wanted a copy - at least as far as we have direct proof. He could have covertly done far worse. The description doesn't seem unreasonable.
Actually, according to the Guardian journalist, Snowden wouldn't give them a copy of everything. You can disbelieve him, but at least on the surface it appears Snowden was being more careful than Chelsea Manning. (and yes, I consider Chelsea Manning a traitor)
There's no debate Snowden stole highly classified intelligence documents and leaked them to the press. But that doesn't mean he's automatically a traitor. He might be, but we don't know. For example, suppose you had highly classified intelligence documents that implicated the NSA in a coup attempt to overthrow our elected leaders or coerce them in some way. Revealing those documents would not make you a traitor; quite the opposite. And for some people, what Snowden revealed shows an unconstitutional and potentially dangerous action by a portion of our government. If they're right, he's no traitor; quite the opposite.
And I'm only talking about the part that reveals blanket monitoring of US citizens, without cause nor due process. Monitoring foreign nationals isn't unconstitutional, and is what we should want our government to do: it's why have the CIA and NSA and so on to begin with. (Sorry Merkel, but monitoring Europeans is fine too, including their elected officials. We're friends now, but haven't always been, and might not forever be.)