Horn is the lone Democrat in Oklahoma's congressional delegation. She reported raising more than $960,000 through June 30.
Horn's closest competitors in the race the 5th Congressional District were Oklahoma City businesswoman Terry Neese, who reported raising $531,000, and state Sen. Stephanie Bice, who reported raising $181,000. Neese's total included a $350,000 personal loan.
Horn pulled one of the biggest upsets in the 2018 midterm election when she knocked off two-term GOP incumbent Rep. Steve Russell and flipped the Oklahoma City-area seat that had been in Republican hands for four decades.
Republicans still outnumber Democrats in the district.
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