California's June 2026 primary election saw over 148,000 mail-in ballots rejected, a significant increase from 2024. This total represents 1.73% of all mail-in ballots cast in the state. The primary reasons for rejection included ballots arriving too late (over 93,000), unsigned ballots (8,300), and non-matching signatures (nearly 44,000). Other, less frequent reasons included lack of photo ID, duplicate voting, missing ballots from envelopes, and multiple ballots in one envelope. Rejection rates varied by county, with Tulare County having the highest at 3.52% and Placer County the lowest at 0.93%. Los Angeles and San Diego counties reported rates of 1.34% and 1.37%, respectively. Kim Alexander of the California Voter Foundation attributed late rejections primarily to late postmarks, not delayed arrival. Former President Donald Trump criticized California's election system following the primary, alleging rigged elections. California Governor Gavin Newsom's office countered Trump's claims, stating voter fraud is rare and emphasizing the requirement for U.S. citizenship to vote. The Trump administration has advocated for stricter mail-in ballot regulations, citing concerns about fraud.