I am going to predict that the SCOTUS won't even hear the case. They don't want to have anything to do with it. But if they do, I don't think it is going turn out the way you guys believe it will. Let's take the arguments,
The office of the presidency is not covered by the 14th Amendment,
"No person shall be a Senator or Representative in Congress, or elector of President and Vice-President, or hold any office, civil or military, under the United States, or under any state, who, having previously taken an oath, as a member of Congress, or as an officer of the United States, or as a member of any State legislature, or as an executive or judicial officer of any State, to support the Constitution of the United States, shall have engaged in insurrection or rebellion against the same, or given aid or comfort to the enemies thereof."
Now tell me, how is the office of the president excluded? Do we need to discuss the meaning of "any"? Seems pretty clear to me. Did Trump take an oath? Pick a side, civil or military, was Trump not the Commander in Chief? That argument is not going to fly.
the insurrection clause is not “self-executing” — meaning Congress alone must enforce it, and states cannot make that determination on their own
I agree, it is not self-executing. But let's turn to the amendment itself.
But Congress may by a vote of two-thirds of each House, remove such disability.
Now that kind of begs the question. If it is Congress alone that is to enforce this clause, why would they even need the power to "remove the disability". It is here that we have to evoke the elections clause within the Constitution, it is the state that controls the election, and the SCOTUS has consistently upheld the state's courts right to interpret the state constitution. Colorado's constitution requires a presidential candidate to be eligible to be president, Michigan's does not.
that by kicking Trump off the primary ballot, the state Republican Party’s First Amendment rights of association have been violated.
Now that one is absolutely comical. The party has the right to nominate any damn fool they want to. The party does not have the right to have an ineligible candidate placed on the ballot for the general election. Could the Republican party nominate a convicted felon? Sure they could. Could they nominate someone that wasn't born in the United States, like the Arnold? Sure they could. Dyo they have the constitutional right to have that person on the ballot? Hell fawking no. I mean here is a thought, actually nominate someone that is eligible.