I don't know that I would advise Snowden to ever come to the US. Pardon or no pardon. And I mean that in a very caring way. The people after him are dangerous, and they don't care about laws, or rights. Think Erik Prince, but actually smart, methodical, and quiet. Oh, and there are thousands of them.
Can you elaborate? Are there murderous independent elements within the NSA and CIA that would do this to an American citizen? I’m a huge cynic, but perhaps too naive about this. That all sounds very scary, especially when the leak was about a very large institutional apparatus that feels too big for anyone to take it personally.
Snowden asserted clearly, on at least two different occasions, on the record, that the IC would not hesitate to assassinate Bart Gellman, a US journalist, if doing so would have prevented the publication or further distribution of the documents Snowden provided him.
Gellman writes about both of these occasions in his book Dark Mirror, which I recommend you read if you’re interested in becoming less naive about the American spy apparatus.
Additionally, the commander in chief of the entirety of the US military, including all of the IC (CIA et al), has plainly stated that Snowden should be executed. Note that Snowden has not at this time yet been put on trial, and the US constitution establishes the presumption of innocence, so such an event if it were to occur would be accurately described, legally, as an extrajudicial assassination of a US citizen.
For Mr Snowden, this is not a game.