The way I read this is that the state requires proof of citizenship before you’re allowed to vote in state elections.
But you’re on the honor system for Federal elections.
Not sure if this is because of past legal rulings or what.
Blame a federal judge.
AZ passed Prop. 200 (2004) “Arizona Taxpayer and Citizen Protection Act” which says you have to prove citizenship to register to vote or apply for services. A judge said AZ has to allow the Federal registration form, which has only the “honor” system.
This is because of a recent SCOTUS decision that held a state can only us U.S. citizenship as a requirement for voting in state elections, but can't enforce it for elections to Federal offices. However, this also creates an easy way for the Federal government to check on whether a person voting in a Federal election is a U.S. citizen, as required by Federal law. All it needs to do is get the AZ "Federal qualified only" list and require each person on thatlist to prove his/her citizenship to ICE.
It is due to a legal ruling that Arizona cannot impose standards on federal elections.
The legal fight has its roots in Proposition 200, a 2004 ballot measure which was part of a broader effort aimed at those not in the country legally...
...But Congress, in approving the National Voting Registration Act, directed the federal Election Assistance Commission to design a single national voter-registration form to simplify the process. More to the point, that form requires no proof of citizenship but only that those signing up swear, under penalty of perjury, that they are eligible to vote.
In 2013, the U.S. Supreme Court rejected an attempt by Arizona to enforce the proof-of-citizenship requirement on those using that form, at least for federal elections.
https://kjzz.org/content/645985/arizona-settles-voter-registration-lawsuit
“By 7 to 2, the Supreme Court justices struck down Arizona’s Proposition 200 as violating the National Voter Registration Act, which requires only a written declaration of US citizenship...
...“We hold that [the NVRA] precludes Arizona from requiring a Federal Form applicant to submit information beyond that required by the form itself,” Justice Antonin Scalia wrote for the majority justices.”
SCALIA ruled against Arizona!