Snowden definitely broke the law and he knows it. Personally I am happy he did because we no longer need to have any illusions, the US is monitoring every non-citizen anyway they can. Our governments should therefore take steps to protect us from this snooping.
Snowden is best off staying in Russia - I don't see why any US administration should pardon him. He's as guilty as Manning in this respect. Its up to a US court to decide in how far his alleged motivations should play a role in reducing his sentence or in how far the limits he imposed on the publication of his revelation affect the severity of his breach of the law.
The US law is sucky for whistle blowers in these cases - you cant get the normal whistleblower protection that you can get in any other case. If someone feels this is not a good system have congress change the law.