Imagine you're a journalist and someone hands you a shoebox full of SD cards with classified materials including video evidence of war crimes. Most of us would agree it is the ethical thing to do to publish that and you're definitely a journalist.
Now imagine you had a contact in the military with acccess to classified data. What if instead of simply receiving that information, you tell that person what you're interested in. Are you still a journalist?
What if you procure tools for that person to bypass security procedures? What if you instruct them on methods they can smuggle out that information from a secure facility? Are you still a journalist?
What if you run someone off the road so they have a car accident and they miss their shift and that person is in charge of facility security, making it easier for your contact to smuggle out classified materials? Are you still a journalist?
This can go on and at some point you're no longer a journalist.
My point is that Assange was allegedly more of an active participant in acquiring these materials so there's an argument to be made that he wasn't a journalist, legally speaking.
But here's where I think Assange really hurt himself: by playing politics in selectively releasing the Podesta and DNC emails to try and sway the 2016 election. This demonstrated that Wikileaks is not, as it portrays itself, a vessel for unfiltered publication. This mattered in the court of public opinion because that's what would ultimately have to come to Assange's aid.
Now make no mistake: the US government did what it set out to do, which was to create a chilling effect on journalism that exposed US government secrets. Assange has essentially spent 12 yaers in confinement between the Ecuadorian embassy and Belmarsh awaiting extradition.