Assange got e-mails for both Republican and Democratic parties from a Russian hacker and then specifically chose to withhold the Republican e-mails

but that’s not what he or his employers wanted.

Why would Russia give him information on both parties if Russia wanted to support one party over the other?

I think you've got things confused. I think the controversy was that he released information on the Democrats, provided by Russia, but then subsequently did not release information on Russia being corrupt. This was then construed as him being in support of Russia, when, by his argument, he simply did not think reporting on Russian corruption was newsworthy - of course Russia is corrupt.

If you can please provide evidence that Assange or Wikileaks were provided evidence of Republican corruption by the Russians, that would be appreciated.