Leave it to the states.
Sorry, that doesn’t work when you consider the equal protection clause of the constitution that so many liberal lawyers are eager to invoke. If as a citizen of the USA I am promised equal treatment before the law, then the law (Federal/State/Local) cannot enfranchise/disenfranchise any particular group vis a vie another. Simply stated, individuals in Union states are treated as a second class citizens in preference to union members. This is simple discrimination by the state. The reason the state practices this discrimination is simply because the unions are easiest source of fast cash for campaign donations. Theorectically, the constitution protects the minority from the majority relative to individual rights. In union states this is ignored. Either you are for equality or you are not. The union states are clearly not interested in treating its citizens equally.