State law already allows challenges to a voter’s registration up to the 90th day before an election, if a person is suspected of lacking South Dakota residency, voting in another state or being registered to vote in another state. The new law adds citizenship as a justification for a challenge.

Challenges may be filed by the South Dakota Secretary of State’s Office, the auditor in the county where the voter is registered, or a voter in the same county. The challenge must be in the form of a signed, sworn statement and must include what the law describes as “documented evidence.”

So the "challenge" this already exists but citizenship is being added as another reason. I wonder what the requirements for evidence are or if some county officials will call the sworn statement itself "documented evidence."