The Wisconsin Elections Commission opened a formal inquiry Friday into missing vote-storage drives from Milwaukee after confirming that five of nine USB devices from city polling sites contained no recorded election results following Tuesday's primary.

Milwaukee is the largest city in a battleground state, and its vote handling has drawn scrutiny in past cycles. City election officials said the missing data posed no serious problem, citing paper tapes and backup records that allowed results to be reconstructed and certified.

The commission's staff will examine chain-of-custody procedures and the handling of memory devices at affected wards. Republican members called for an independent audit, while Democratic members urged caution against amplifying unproven claims of misconduct ahead of the November midterms.

Republican lawmakers in the Wisconsin State Legislature said they would seek testimony from Milwaukee's election director, arguing the episode underscored the need for tighter oversight. Voting-rights groups, including the League of Women Voters of Wisconsin, warned that partisan framing risked eroding public confidence without evidence of tampering.

Wisconsin's presidential margins have been decided by fewer than 30,000 votes in recent cycles, making Milwaukee's administration a recurring flashpoint. The commission said it expected preliminary findings within weeks, before certification deadlines for the primary results.