I don’t know if I’d resort to executions, but some prison time is definitely in order (done alongside violent criminals, not in some min security facility), along with permanent revocation of voter registration.
What is the difference between putting a gun to your head and preventing you from voting; or committing voter fraud? What is the difference between a political coup, or voter fraud? Either way, the will of the people is thwarted by a small group of individuals, who in turn impose their will upon the population.
I view this as more heinous than simply murdering a dozen innocent people; they are denying the most basic rights of millions of people. I don't hold their lives in such high esteem; I say send them to God to determine their eternal punishment.