Why would Russians want to hack into voter date bases?

With evidence Russian hackers have breached or attempted to breach voter data information in two states, the question is:
Now why in the world would the Russians want to do this? It is no secret they favor the election of Donald Trump and it is no secret that Donald Trump's foreign policy as outlined to date is more in the Russian national interest than in America's. Both Trump and Russia want to end NATO as we know it, which would ease any Russian further encroachment into the Baltics, Moldova, and Romania by removing a threat of western military counter action. Trump wants to retreat from alliances, a neo isolationist policy that would weaken the United States from an ability to be a player in world leadership and in forming alliances that would also benefit our national interests. His business interests have looked to Russia and until recently, his campaign manager had also served as an advisor the deposed president of the Ukraine now in exile in Russia.