Wikileaks' current agenda appears to be to disrupt Western governments through leaking damaging information. I don't see a clear preference for political parties; the Manning leaks were damaging to the Republican Bush administration.
I believe that the most probable source of the DNC leaks is Russian government units, but not for the purposes of election manipulation. Here is an article that most credibly posits this theory: https://themoscowtimes.com/articles/russian-spycraft-how-kre....