Calfornia cannot add to the requirements for federal offices laid out in the Constitution.
Democrats simply dont like Republicans being allowed to vote for Trump but there wont be a state primary.
This concerns the general election.
I agree with your premise, but California is not required by the U.S. Constitution to hold a popular vote for President of the U.S. The state legislature if free to allot the state’s electors in a manner it sees fit. In fact, I can see advantages to CA’s keeping PDJT’s name off of the ballot:
It shows how ‘undemocratic’ the dems are when it comes right down to it.
It makes any discussion of total ‘popular vote’ moot.
It causes a reaction against dems in other states (sorry California, but there are other states).
It will be fun to watch the lame stream media try to defend it
All that said, I hope CA is required to put President Trump’s name on the ballot just to pay them back for all of many lawsuits against his E.O.s and policies.