Exactly, each state runs their own election and have their own rules on how they are run and counted so in theory SCOTUS should recognise that and allow them to do as they have always done. As you said they gave the states the right to determine their own abortion laws so could he a bit hypocritical
I think SCOTUS is considering this from the point of view that the presidency is a federal office and the states should not interfere, but they will have to find some sort of off ramp and keep in mind this will set a precedent.
In the oral argument there was not much said about the insurrection but I wonder if SCOTUS will take that into consideration and say yes an insurrection and rule Criminal Defendant is barred from being on the ballot
Keep in mind SCOTUS is also dealing with the immunity plea at the same time so they have a lot to consider, though there is no way SCOTUS will rule that presidents have immunity
