Even if that’s true — it’s not, no emails have been shown to be fake — it’s not illegal to publish false information.
And publishing false information is not illegal. Knowingly aiding a foreign government in their efforts to undermine an election is treason.
Assange is not a US citizen.
I've definitely read several news articles that say he stands accused of both treason and espionage, though. I do wonder how that works for a foreigner. Has he ever even been to the United States?
[1] https://arstechnica.com/information-technology/2016/06/gucci...