Chicago’s Choice Points to a Democratic Divide the G.O.P. Hopes to Exploit

And that has included a pitch for more school choice, whether through charter schools or vouchers to help public school students attend private schools. Again, Mr. Vallas and Mr. Johnson represent polar opposite positions on the issue: Mr. Vallas, as Chicago’s schools chief, expanded charter schools, then virtually eliminated neighborhood public schools when he took over the New Orleans school system after Hurricane Katrina. Mr. Johnson, a former schoolteacher and teachers union leader, stands firmly against that movement.

“This is a microcosm of a larger battle for the soul of the nation,” said Delmarie Cobb, a progressive political consultant in Chicago, “and being the third largest city, it’s going to get all the national coverage. This is going to be an intense five weeks.”

For the national parties, those five weeks will be tricky. The runoff between Ms. Bass and Mr. Caruso in Los Angeles forced the Democratic establishment to get behind Ms. Bass, a known quantity with a long career in the House of Representatives. If the Democratic establishment rallies around Mr. Johnson, the outcome of the Chicago mayor’s race could mirror Los Angeles, come Election Day.

But Mr. Johnson’s ardent progressivism, including his outspoken skepticism of policing as the answer to rising crime, could make him toxic to Democrats with national ambitions, including Illinois’ billionaire governor, J.B. Pritzker.

Likewise, Mr. Vallas’s pledge to beef up Chicago’s police force and unshackle officers from the controls put on them after high-profile police shootings like the killing of Laquan McDonald could make him a hero of Republicans eying a run at the White House next year. But their endorsements would run counter to Mr. Vallas’s efforts in the nonpartisan mayoral race to persuade Chicagoans that he really is a Democrat.

Though Mr. Johnson’s 20.3 percent on Tuesday put him well behind Mr. Vallas’s 34 percent, he enters the runoff perhaps as a slight favorite. Mr. Vallas was the only white candidate in the field, while Mr. Johnson had a half dozen Black competitors, including the incumbent mayor, Lori Lightfoot. Many Latinos who voted for the only Hispanic in the race, Representative Jesús García, who is known as “Chuy,” are likely to gravitate to Mr. Johnson.

But events over the next five weeks — a mass shooting or other horrific crime — could reshape the debate. Regardless, national Republicans, eager to make the crime debate central as they joust with each other for their party’s presidential nomination in 2024, are not likely to stay quiet.