Thousands believe that Dick Cheney is guilty of war crimes, but as far as I know, no one has tried to kill him yet.
I wouldn't completely rule out the idea that someone might take a shot at Snowden were he to return, but at the same time I doubt that the vast majority of people who label him a "traitor" feel strongly enough about it to personally try to kill him.
> but as far as I know, no one has tried to kill him yet.
I'm not sure that's quite apples-to-apples, given: (1) US political asymmetries; (2) nobody accused him of conspiring with a clear "The Enemy"; (3) Cheney was already a multimillionaire with private security and moving in rarefied social circles.
If Cheney was once hunted by the US government, widely accused of being a communist spy, and he shopped for groceries like a regular person, I imagine the odds of an attempted attack would increase.
The US political asymmetries include that gun advocates, peace officers, and ex-military types that probably dislike Snowden most are statistically the least likely Americans to commit violent crime and have not engaged in any kind of systemic political violence in the modern era. It's the left that plans and starts riots e.g. at Trump rallies as WikiLeaks has documented.
Only crazies and communists and white supremacists have used assassination as a political tool in America in the modern era and that hasn't even happened in forty years.
I expect Snowden would be perfectly safe under a pardon. Until then I'd advise him to avoid long sight lines; America's official enemies have a way of finding themselves exploded at a nice sterile distance.
The problem with that statement is a lot of Americans would be foaming at the mouth if you labelled them a liberal due to a severe misundertanding of the meanings of words like 'liberal', 'progressive', 'communist', 'socialist'.
I wouldn't completely rule out the idea that someone might take a shot at Snowden were he to return, but at the same time I doubt that the vast majority of people who label him a "traitor" feel strongly enough about it to personally try to kill him.