In this NYTimes survey of security experts about potential risks to the election process and ways to forestall them, I think this suggestion from Michael Chertoff is worth highlighting:
But defenses are not perfect, so we also need ways to recover in case of a breach. Election officials should periodically download registration data to systems that are not connected to the internet and identify all the underlying infrastructure that needs to run for everything else to work. Even better, election officials should frequently generate paper records of registration data, which can be used as a last resort. While manual processing is slow, it is demonstrably reliable and available.