And? He’s not a US citizen, nor is he in our country.
Espionage charges can be levied against non-citizens, it happened frequently during the cold war. At that, the Supreme Court ruled in Schenck v. United States (1919) that the act didn’t violate the first Amendment (as Assange’s defenders are hiding behind). At that, the Schenck case is interesting in this discussion because he received information, in his case, rolls of who would be drafted, and published those.
See USC 18, Part 1, Chapter 37, Subsection 798.