JFK for sure, Truman alleged...likely others. Plus many many down-ticket. "Vote early and often" has been their mantra for a long time.
Hell...the KKK was developed to keep blacks from voting for Republicans.
New York City, Tammany Hall
Different era, different methods.
November 2020, seems the crooks deploy high tech methods and foreign actors, China, Italy, Switzerland, England, Germany, all teamed up to select the US President