Cheating is a high risk, low benefit enterprise. It's rare, and usually unintentional.
The party promoting unpopular policies tries to impede voting by demographics unlikely to support it. It makes wild claims of cheating by opposing voters. It seeks to wipe large tranches of opposing votes from the official count.
Repeat an unevidenced claim often enough, and from enough sources, and the public begins suspecting there must be some truth to it. When investigated, though, these allegations rarely come to anything statistically relevant. The Republicans claim thousands of deceased voters, and investigation uncovers two. They claim widespread tampering with voting machines, and investigations find no supporting evidence, with hand recounts of ballots in agreement with machine counts.
But what else is a party supporting a platform of unpopular policies to do?