"The reader’s brother, a San Bernardino County resident, received official communication urging him to register with a specific political party in order to participate in the presidential primary via mail-in ballot." Presidential Primary. Democrats use no registration voting to choose the weakest Republican by voting in Republican primaries. The Democrat candidates are already determined by committee. Their primary vote is just theater. https://www.washingtonexaminer.com/dnc-argues-in-court-we-dont-owe-anyone-a-fair-primary-process