Well, yes, the obvious. They revealed classified information and thereby discomfited portions of the US government. That has been discussed at length hereabouts and elsewhere.
The non-obvious and not-much discussed, though, is this:
Neither one of these men should have been cleared to the information they revealed, and it is the fault of movement conservatism and George W. Bush that they did have such access. That is, the very people most likely to call Snowden and Manning traitors are the people who made their "treason" possible.
More below the Orange Squiggle of Power.
First, the unfortunate Bradley Manning. I wrote about Manning in June of 2011:
You may read the diary, but a brief synopsis is that Manning showed numerous signs of mental instability prior to deployment. He should not have been a soldier, much less a soldier with access to sensitive information.
As for the Phantom of Moscow Airport, his clearance was not done properly. The government had outsourced this rather vital function in the name of saving money. And, of course, Snowden was an employee of Booz Allen Hamilton rather than the USG - again, in the name of saving money.
The same Snowden who made $200K / year to work as a system administrator. If you are unclear about how that sort of pay scale saved money you are not alone.
How, then, is this the fault of the conservatives and Dubya? It's pretty simple: even in the one thing conservatives claim to believe government should do - national defense - they are unwilling to actually increase the size of government or raise taxes.
In Manning's case, it was rather obvious by the time he enlisted that the United States either needed to fish (get the hell out of Iraq) or cut bait (put in the number of troops the Pentagon originally said they needed to actually "win"). The first required the utterly depraved Bush to admit he had made a mistake. The second not only required said admission, but also would have required a much larger army, which in turn would have required a draft and increased government revenues.
Bush, being the coward and weakling that he is, stubbornly refused to chose either to quit or to attempt to win. That led to an incredible burden on the Army, which led to retention and recruitment problems, which led to a young man who got so upset prior to deployment that he actually wet himself in public being kept in the Army and sent overseas, and in the course of events being cleared. It also lead to the deaths and crippling injuries of thousands of Americans, hundreds of thousands of Iraqis, the strengthening of Iran, trillions of dollars in debt, higher oil prices and a drag on the world economy, and a few other bad things.
The case for Snowden is even clearer. Post 9-11 it was pretty clear that the US needed to collect more intelligence regarding Al Qaeda and possible terrorists, and to make better use of the intelligence we did collect. Note well that in no way do I intend to make the slightest defense of the Patriot Act, the creation of the Department of Homeland Security, or any of the other things done to (allegedly) further that goal of better anti-terrorist intelligence. I simply note that 9-11 was a bad thing and that trying to prevent similar events was a legitimate function of the US government.
So, you would expect the government to actually hire some people to perform these intelligence collection and analysis functions. And they did hire some people - a fraction of those needed for the new tasks. The rest were contractors, such as Snowden. Because even when faced with the worst attack on US soil since the end of the Civil War, movement conservatives and GW Bush could not bring themselves to hire government employees (who might well be UNIONIZED) and increase the overall number of government employees. No, "shrinking government" was more important than performing a vital task well.
So, here we are. Two men, leaking information that conservatives would have preferred not be leaked, who would never have been able to do so had it not been for an anti-government conservatism so unhinged that it even attempts to privatize national security. And the sad thing is that the conservatives will never recognize it, nor would they admit it if you pointed it out to them. Nevertheless, Snowden and Manning are poster boys for the utter intellectual bankruptcy of anti-government conservatives.
Irony still lives.