Perhaps there is a lesson to be learned from Canada.
Whenever there is a Federal Election is called in Canada, thousands of paid volunteers go to every house, apartment in every village, farm town, city and ask people to show proof of their citizenship. Once it is shown, the respondents receive a piece of paper, indicating where their polling station is, authorizing them to go there on election day, show the paper and vote. They don't ask the respondents if they are Conservatives, Liberals or NDP, or Green, because the way a person votes is between the person and the ballot box, not the pollsters.
And voting is on a piece of paper showing the names of candidates. No fancy one-arm bandits, no hanging chats, no computers, just a simple single "X" next to one's favorite candidate's name.
No voting results are shown, until the entire country voted and all polling stations from east to west are closed.
Votes are counted manually and within three hours most results are known.
BTW, while it seems foolish that there are no fixed election dates in Canada, remember there are also no two year long expensive, hate-filled and overly long election campaigns.
Can anyone tell me why can't ALL primaries be held on the same day, one month before the Convention, which should be no more than one month prior to the Election?