Instead, in state after state, the GOP takes a knee, and begs the Democratic Party, and state government, to set the rules.
The first step is to have voter registration by party, which roughly half of the states do not. Without that, there cannot be “closed” primaries.
And even when there is registration by party, and primary participation is limited to party members, Democrats can still switch (temporarily) to infiltrate GOP primaries. Of course we could do the same, but it’s funny how that sort of thing seems to go one way only for the most part.
But if there is to be *any* chance at purity, there has to be party-level registration.