A federal judge heard arguments today in a case to decide whether California should have to give the federal government sensitive data about its more than 23 million voters.

California is one of 14 states the U.S. Department of Justice has sued in recent months in a nearly nationwide effort to collect voter data, including sensitive information that typically is under state control and kept private.

The California case is further along than any other, so it serves as a kind of test that’s being closely watched by election officials, voting rights advocates and election integrity hawks. The U.S. Department of Justice has requested complete voter registration data from at least 40 states.

Here's a closer look at the legal showdown — and why it ultimately might be decided by the U.S. Supre

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