Five former Governors of Delaware have filed this amicus curiae brief in the U.S. Supreme Court, asking the court to hear Carney v Adams, 19-309. This is the case over the Delaware law that says no one is eligible to be appointed a state judge (for most of the state courts) unless they are a member of a party that has at least 5% of the registered voters. The ex-Governors support the law, which the Third Circuit invalidated a few months ago. Two of the ex-Governors are Republicans, and three are Democrats.
Obviously the Delaware law makes it impossible for any registered independent to become a state judge.