How do you show that in a six person race?
Shift the ineligible candidate's votes among the others, and see if it affects the outcome. A do-over might be avoided if those left standing reach a settlement.
If the ineligible candidate was otherwise the winner, and 2nd and 3rd are close together, I see no way to avoid a do-over, in order to pick a winner. Same sort of calculus can play down-ballot, too.
Complicating things in a primary, there is no way for a court to know the delegate margin at the nominating convention. All any court has potential control over is the delegates selected by election in that state.