Speculation surrounding Giannoulias' bid has been circulating for the past couple of months.
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"The hardworking people of Chicago deserve a government that works just as hard as they do," Giannoulias said in a campaign video. "Chicagoans don't expect perfection. But they do expect leadership that listens, that rolls up its sleeves to work hard, and that loves this city as much as they do. Leadership that has solved problems and will continue to solve problems."
Giannoulias is set to have a campaign rally in Bronzeville at 12:30 p.m. Sunday.
The Chicago mayoral election will be held on Feb. 23.
This is a developing story; check back for details.