Unfortunately, the supreme court has zero checks and balances, and recently has been willing to make partisan political rulings, so it may well strike it down to help Republicans.
They can. They have. They will again. The states have the constitutional right to select their electors as they choose, but this court has demonstrated complete contempt for justice and fairness.
The supreme court also overruled states trying to ban interracial marriage, implement poll taxes to unfairly target poor people, and place signs in their yard protesting war.
The only easy grounds for them to do so with an actual constitutional backing would be that interstate compacts are supposed to be approved by Congress.