"unsubstantiated claim"
Voter fraud was rampant, esp in Cali, during teh 2016 primary.
The majority of said fraud was a DIRECT result of mail in votes being tampered with.
sauces
https://observer.com/2016/07/california-calls-fraud-demands-dnc-investigation/
https://soapboxie.com/us-politics/Election-Monitors-in-San-Diego-Catch-Whited-Out-Sanders-Votes-on-Film
https://www.commondreams.org/news/2016/06/10/after-frustrating-primary-millions-ballots-california-remain-uncounted