CHICAGO (CBS) — An already crowded field in the race to become Chicago’s next mayor is about to get even larger. Cook County Board President Toni Preckwinkle will officially announce her bid to replace Rahm Emanuel on Thursday afternoon in the Kenwood neighborhood.

Preckwinkle flirted with a run for mayor four years ago, but ultimately decided not to challenge Emanuel.

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Her campaign kickoff on Thursday comes one day after announcing she had forced out her chief of staff, John Keller, for engaging in “inappropriate behavior on his personal time.”

In a statement Wednesday afternoon, Preckwinkle said she learned about the allegation against Keller on Friday, and when she confronted him, he did not deny it. She then demanded and received his resignation on Tuesday.

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Preckwinkle is the second high-profile candidate to jump into the race for mayor this week. Gery Chico, who ran against Emanuel in the 2011 race for mayor, threw his hat in the ring on Tuesday.

Chico, who served as longtime Mayor Richard M. Daley’s chief of staff, president of the Chicago Board of Education, and head of the Chicago Park District and City Colleges of Chicago, has said those experiences make him the most qualified candidate in the race.

Violence reduction, education, and jobs are expected to be the main issues he’ll push when he sits down for a series of media interviews on Thursday.

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At least a dozen other candidates have announced bids for mayor, including former White House chief of staff and Commerce Secretary Bill Daley, Cook County Circuit Court Clerk Dorothy Brown, former Chicago Public Schools principal Troy LaRaviere, former Chicago Police Board president Lori Lightfoot, former Chicago Police Supt. Garry McCarthy, former CPS Chief Executive Officer Paul Vallas, millionaire businessman Willie Wilson, policy consultant and former 2015 mayoral candidate Amara Enyia, community activist Ja’Mal Green, attorney Jeremiah Joyce Jr., former City Council candidate John Kozlar, DePaul University student Matthew Roney, and tech entrepreneur Neal Sales-Griffin.