The US Supreme Court on Monday rejected the Trump administration's emergency request to make California set aside mail-in ballots cast by any of about 20,000 registered voters whom federal officials say are likely not US citizens.
The decision, issued hours after the Justice Department filed its request, leaves previous lower court rulings intact ahead of Tuesday's midterm elections, which will determine control of Congress.
The Justice Department sought to separate the contested ballots from other votes until authorities could establish whether the registered voters were US citizens.
Federal officials argued that counting potentially unlawful ballots could undermine legitimate votes and complicate subsequent challenges.
The dispute originated from a federal list of about 20,000 registered voters whom the government suspects of being noncitizens.
California officials disputed the reliability of the information, warning that inaccuracies could result in eligible voters being disenfranchised.
The Justice Department filed its lawsuit on October 15, alleging that California obstructed federal enforcement of laws prohibiting noncitizen voting in federal elections.
State officials maintained that existing election safeguards adequately address voter eligibility.
US District Judge David Carter rejected the administration's request on October 28, questioning the reliability of its evidence and criticizing federal pressure on state election authorities.
The Ninth US Circuit Court of Appeals refused to intervene on Friday, October 30, in a 2-1 ruling. The majority upheld the district court's finding that the ballots of specific individuals could not feasibly be identified and separated, the Associated Press reported. Judge Patrick Bumatay dissented, writing that California "says it can do nothing to prevent illegal voting."
The Supreme Court issued its rejection without explanation, and no justice publicly dissented.
The decision comes amid broader administration efforts to challenge voting procedures, particularly mail-in ballots.
Multiple studies and state audits have found that noncitizen voting is rare.
California holds 52 seats in the House of Representatives, making it a significant battleground as Republicans seek to retain congressional control.
Democrats need a net gain of four House seats to secure a majority.
The ruling allows California to proceed with counting ballots under its existing election procedures.