Assange said if he was given stuff to leak about Trump and was able to verify it the same way he verifies anything, he would release it. There's no reason not to, it's not like Assange is the only person in the world capable of releasing stuff and performing journalism. The idea that he covered up Trump leaks is ridiculous - the leaker would just go to someone else and it'd get out regardless. This is proven by the many many Trump leaks that did get out to mainstream media.