States can have their own rules for how one gets on a ballot, but they just can't bar candidates from the ballot just because they don't like them, that kinda falls under the constitution...The SCOTUS were likely to overturn it because it would be politically dangerous to allow it. There's no solid or unambiguous federal law that prevents states barring candidates for state primaries-- I notice you've been unable to cite one.
And of course, you also claimed that states can't rule on cases arising from federal law. Which has now been comprehensively shown to be bullshit.
You're take that it's likely that SCOTUS will allow states to determine for themselves is even more bullshit.
States do have broad authority to set how one gets on the ballot and as long as someone follows those rules, they get on the ballot. States can't deny people to get on the ballot that follow those rules just because.Like Silvanus said, states have pretty broad authority over how they run their elections, including ballot access. Which presents a reasonable argument to remove Trump from the general election ballot being a valid thing a state can do (for the same reason they don't have to include every third party candidate). Since primaries are private organizations borrowing state election infrastructure to decide who to back, it's arguable that the state might have less say so about who's on the ballot for those.