In 2016 the relationship between Julian Assange and the US is about as hostile as possible. He was seeking asylum against this very extradition process that is ongoing. A big part of that drama was also that the US secretary of state under the previous years, ie the U.S. government's minister of foreign affairs, was a candidate for the 2016 presidential campaign and thus is it likely that there is a personal grudge between Assange and her.

And he was given documents that could hurt her. He used them.

It seems pretty clear that neutrality has not been on the tables for Assange ever since he sought political asylum. As pointed out above, this does not mean he has fabricated documents, or knowingly distributed fabricated documents, but since 2012 he has been in an active conflict against the government of the USA and in particular the foreign affairs side of it and thus leaks should be seen in that context.