Assange is being charged under a century-old law passed in order to criminalize dissent to US participation in WWI. I came across this randomly during my pandemic reading (The Great Influenza, about the Spanish Flu of 1918). It was really shocking to read how thoroughly the US government suppressed speech during WWI - it's not something I was at all aware of before.

The Espionage Act is almost certainly unconstitutional, though it's still on the books. Ever since the Vietnam War, there's been a tacit understanding that the government will only use the law to go after government employees who leak information, but that the government won't prosecute the people who publish the information. With this prosecution, the Trump administration is breaking that understanding. The precedent is being set that whenever a newspaper publishes, "Sources tell us..." or "According to documents viewed by...," they're opening themselves up to criminal prosecution.