The KKK wouldn't attack black people to terrorize them into voting Democrat, they'd attack them to keep them from voting at all.
"The Klan terrorized black Americans through murders and public floggings; relief was granted only if individuals promised not to vote for Republican tickets, and violation of this oath was punishable by death," he said. "Since the Klan targeted Republicans in general, it did not limit its violence simply to black Republicans; white Republicans were also included." (emphasis added)