To win a second term, Mayor Brandon Johnson will have to overcome a serious challenge from perhaps a dozen candidates, including Illinois Secretary of State Alexi Giannoulias. Mayor Brandon Johnson files signatures on Oct. (Heather Cherone / WTTW News) Mayor Brandon Johnson made his bid to become the second Black man to be reelected Chicago mayor official Friday afternoon, telling reporters he had gathered 33,000 signatures from Chicago voters to qualify for.