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Brunner has served on the 10th District Court of Appeals since late 2014 and also previously served as a Franklin County Common Pleas Court judge.
She was elected secretary of state in 2006, defeating Republican Greg Hartmann, and served through early 2011.
Instead of seeking re-election, Brunner opted to run for the Democratic nomination for U.S. Senate in 2010, losing to then Lt. Gov. Lee Fisher, who then lost to Republican Rob Portman.
O’Donnell announced his plans to run months ago. A Cuyahoga County Common Pleas Court judge since 2003, O’Donnell lost to Republican Justice Patrick Fischer in 2016 and also was defeated by French in 2014.