Every state has its own rules—they are all over the place.
In the case of Michigan and Nevada and a few other places Democratic legislatures played games and ordered primaries when Republicans did not want them—so then the Republicans responded with both primaries and caucuses—but tilted the delegate awards to the caucuses.
The Democratic legislation required open primaries so Democrats and Independents could cause mischief in Republican primaries—obviously the Republicans wanted to minimize that damage.
I recall that being the case in Nevada but I did not know it also applied in Michigan. The official GOP excuse for the MI caucus seems to be that they were afraid of too much crossover voting (obviously to help Nimrod) in the primary.
Yet there was also drama about which of the 2 caucuses today was the “real” one. And still Trump apparently got 98% altogether, LOL. I guess the MIGOP isn’t as disunited as the Democrats had hoped for. Yet they are still a disaster organizationally and financially.
I voted in Texas yesterday. As I was walking toward the precinct, a candidate approached me. He was a Democrat running for Congress, in my district. It's now a 75% Democrat district, thanks to redistricting.
He seemed friendly enough, so we chatted for a few minutes. My friendliness ended abruptly when I saw the "Free Palestine" button on his shirt.
I lit into his a$$, shocking his son and a friend of his son. In response, he said "he's for the humanity of it." I bluntly told him Hamas has no humanity, they need to be eradicated from the face of the earth."
After another weak, mealy mouth, excuse, I ended our conversation with, "I know my history, and I've been to Dachau twice. I support Israel 100%. Good day, sir!"