He was unquestionably guilty of unauthorized disclosure of classified information. If he’s tried for that in isolation without being able to present any extenuating circumstances to the jury - which is the way that the US Government wants it - it will not be a fair trial.
Espionage, by contrast, is a much more serious crime, indeed a capital one. It is the crime of disclosing military secrets to enemy powers. The Cold War espionage cases (such as the Rosenberg trial) actually stand on a rather shaky legal footing. A modern case would actually be sounder, since the President can arbitrarily designate any foreign nation or person as an enemy since the AUMF of 2001 - which was legally a Congressional declaration of war against the entire world.
How such a case would play out in practice is unclear. Possible outcomes run an entire gamut from simply having Snowden disappear or suddenly suffer a “catastrophic medical event” to being confined effectively forever as the government is granted infinite extensions to prepare its case against him, to a show trial and multiple consecutive 99-year sentences (or even execution), to a show trial with jury nullification, to an executive pardon.
I think the most likely outcome would be that the government security people would be unable to resist committing the same sort of crimes that were committed against Daniel Ellsberg, his attorneys, and even his psychiatrist - crimes which in the judge’s opinion irretrievably tainted the government’s case. And this despite the fact that they could simply advance Permanent Record as a public confession!
The second most likely outcome would be that a trial would go on for years in haggling over the provisions summarized in https://fas.org/sgp/jud/judges.pdf - possibly even ending in multiple mistrials and restarts as jurors are forced to leave because they fall ill or otherwise must be excused from service - with Snowden imprisoned during the entirety of the proceedings. (The government’s anti-trust prosecution of IBM, back in the day, failed on just this sort of jury exhaustion; before the case was decided, changes in the business climate had mooted the case.)
The least likely outcome would that he would be allowed to present a defense including his motivations and the extenuating circumstances. (If memory serves, effectively silencing an espionage defendant from presenting motivations was upheld on interloculatory appeal in the Ellsberg case, which would have been open-and-shut except for the fact that Ehrlichman and company screwed the pooch.)
Is he guilty of unauthorized disclosure? Almost certainly. Is he guilty of espionage. Certainly on the technicality that some of the reporters to whom he made disclosures were not US persons - and therefore enemies because we’re at war with every other nation on the globe. Do defendants who are almost certainly guilty retain a right to tell their story in open court, and to require the government to prove its case against them? Our President has repeatedly made statements like, “they gave up their right to a fair trial when they…”, so at least he believes that the right to a fair trial is not inalienable.
Will he get a fair trial? It’s hard to imagine such a thing’s being possible. Would surrendering for trial yield a just outcome? Even less imaginable; in fact, in the current climate of public opinion and government policy, I would imagine that extrajudicial punishment up to and including out-and-out torture, would precede conviction - and a lynching by parties unknown is not out of the question.
Much more is at stake than Snowden’s guilt or innocence. The US legal system is ill-suited to the resolution of political crimes.
