I had to look up the story again.
I do not see any claims that they told people how to vote but they did say (according to witnesses) things like "you are about to be ruled by the black man, cracker" and similar bile. That plus they were dressed in paramilitary gear, with party insignia and brandising clubs. As a person that they would target that kind of speech towards, yes I would feel threatened.
Clearly an attempt to intimidate voters.
The notion that a couple of black guys would try to start physical violence at a voting station in the USA is a sign you really don't understand race in our country.
Everything about how you described their behavior was aggressive and hostile, particularly to those who were white (using racial slurs) and who did not support Obama's reelection. When people are being aggressive and hostile I don't assume all their actions will be rational or predictable. If someone was to respond to their actions with similar actions (making racial slurs and gloating about the power imbalance between whites and blacks despite who the president is) are you sure there wouldn't have been any violence?
Why do liberals care when children die from a gun but have no compassion on the hundreds of babies that are aborted each day?
I feel extremely sad for both children in each case.... who never get to experience life's journey.