we knew russia had infiltrated voter rolls and registries over a year ago. this goes two ways:
1. they unregistered people in key areas of certain states to help swing things. either it gets trump elected or it gets caught and throws the entire US electoral system into question. it's' a win/win for russia. something like 80k people across three states swung the entire election to trump so it isn't that unlikely. more people then that get taken off the rolls in states legitimately every year.
2. the voter information from those roles was given to cambridge analytica which is how they were able to target with uncanny accuracy the people they felt would be most likely to flip to trump and those most likely to become demoralized and stay home.
wild card: a combination of the two.