Here, here and here. It is a battle over who gets the spoils of election victory. And the election edge to do one party's mischief, or the other's. Biasing the voter pool, as feasible, is a form of non-punishable election fraud each party works at, in terms of getting an upper hand - same day registration favors Democratic vote counts, in general; placing impediments disadvantages the Democrats, to the benefit of Republicans. All else written or argued is off point and intended to misstate and mislead. Which is "fraud."
Your papers, please.