I think you’re correct in your assessment of what the arguments will centre on for the case.
My understanding is that there’s basically three main arguments against:
1. The President isn’t an officer - a complete hogwash opinion quite rightly overturned by the Colorado Supreme Court. The President is referred to as an officer plenty of times in the corpus of law and the constitution.
2. What Trump did doesn’t count as an insurrection - the argument here is that as Trump didn’t physically take part in the march on the capitol or because it wasn’t prolonged enough, that Trump’s actions don’t qualify. Again I think this argument is bunk to anybody with a brain.
3. The 14th amendment is ambiguous about due process - this is one of the major contentions of those who voted against in Colorado. It’s not at all clear what amount of process the constitutional right to be on the ballot requires. Some argue Trump got a trial, had the opportunity to provide evidence and statements, it was heard by a panel of judges and they deemed that he incited an insurrection so that is his due process - it is certainly more than you might see in some civil proceedings. Others will argue that removing somebody from a ballot should require the same due process as one would receive under criminal conviction like the right to a jury trial. This is a genuinely ambiguous and arguable part of the 14th amendment.
If the SCOTUS votes against then it will be under the guise of Trump not receiving sufficiently robust due process - and if this is the case they might attempt to set the standard that needs to be met (e.g. a criminal conviction relating to insurrection). If they do this then Trump could still be barred from holding office at a later date if he is convicted (at the state level so he can’t pardon himself), which could cause all kinds of chaos.
