— hacking DNC network with malware
— exfiltrating voter registration servers
— infiltrating election machine vendors
— CambridgeAnalytica/SCL
— NationBuilder
— scraping FB
— knowing about unsecured code repositories with sensitive credentials like AggregateIQ who built RIPON software for GOP/PACs
(These two possibilities are known thanks to @VickerySec of @UpGuard)