Chicago Votes on a New Mayor. Either Way, an African-American Woman Will Win.

Ms. Lightfoot had a head start on the campaign trail, declaring her candidacy for mayor in May 2018, when it was widely believed that she would face off against Mr. Emanuel.

A relatively unknown figure who has never held elective office, Ms. Lightfoot has spent time introducing herself to voters as a candidate who would focus on overhauling the police department, curbing street violence and rebuilding neighborhoods beyond the affluent downtown and North Side. Ra Joy, an entrepreneur in Chicago who was a candidate for lieutenant governor in 2018, endorsed Ms. Lightfoot early in the race, he said on Saturday at a candidate forum at the Rainbow PUSH Coalition on the South Side.

A mayoral contest between two African-American women has scrambled the usual political calculus in Chicago, or what Mr. Joy called “tribal voting,” in which politicians could count on support from voters of their own race.

“It’s turned that notion on its head,” he said, adding that the successful candidate would have to build coalitions of Latinos, whites and African-Americans in a city where the population is almost evenly divided among the three groups.

Celestine A. Strain, 46, a hospital technician, brought her granddaughter Kalicia, 9, to the forum at Rainbow PUSH, hoping Kalicia would someday remember seeing two black women running for mayor of Chicago.

“It’s amazing for her to see,” Ms. Strain said, adding that she was hoping Ms. Preckwinkle, who has been a familiar face in county government for years, would emerge victorious on Tuesday. “I really believe that she has the right experience.”

The Rev. Jesse Jackson offered no endorsement in the race, saying that he hoped to be more of a peacemaker after what played out in recent weeks as a bitter campaign. On stage on Saturday, he urged both candidates to sign a statement agreeing to appear together the morning after the election. “I wanted to play a reconciling role,” Mr. Jackson said in an interview in his office at Rainbow PUSH. “The campaign ends. Let the healing begin.”