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Democrats and voting-rights groups have challenged the proposed rule as a harmful federal intrusion that could affect millions of voters who cast their ballots by mail.

By Adam Sella and Nick Corasaniti

Adam Sella reported from Washington, and Nick Corasaniti from New York.

The U.S. Postal Service has proposed a new rule that would allow it to refuse to deliver mail ballots in states that don’t turn over voter rolls to the federal government.