CHICAGO — Brandon Johnson had an issue. In a crowded Chicago mayoral race stuffed with established liberal politicians — a sitting congressman, the incumbent mayor, two Metropolis Council members — many citizens had by no means heard of Mr. Johnson, a county commissioner from the West Aspect.

However he had one thing these different contenders didn’t: the Chicago Lecturers Union.

Liked and loathed, the academics’ union has emerged during the last dozen years as a defining voice on Chicago’s political left, placing forth a progressive imaginative and prescient for the town that extends effectively past its school rooms. After extremely public fights with the final two mayors that led to work stoppages, union leaders see in Mr. Johnson an opportunity to elect certainly one of their very own, a former trainer who shares a purpose of rebuilding Chicago by spending extra on colleges and social applications.

Boosted by the union’s endorsement — and maybe extra critically, its cash — Mr. Johnson, a paid C.T.U. organizer since 2011, faces Paul Vallas, a former public college govt who has way more conservative views on policing and schooling, in an April 4 runoff. With the 2 finalists coming from reverse ideological ends of the Democratic Social gathering, the runoff will check whether or not voters favor Mr. Vallas’s plan to crack down on crime, rent extra cops and broaden constitution colleges, or Mr. Johnson’s name to spend extra on public schooling and social companies, add new taxes and look to neighborhood colleges as an engine for broader social change.

“Our college communities actually are a microcosm of the entire political issues that exist,” stated Mr. Johnson, who taught social research to center schoolers in Chicago’s Cabrini-Inexperienced public housing advanced, and who ceaselessly refers back to the time a scholar raised her hand and informed him that he needs to be educating at a great college, not hers.

“It was in that second the place I acknowledged how a lot our system has failed, the place our college students and our households can acknowledge high quality, however don’t consider that they deserve it,” Mr. Johnson stated in an interview. “And so the place I’m immediately is the results of that second.”

Mr. Johnson, who’s on depart from his job with the academics’ union, entered the sector in October with low title recognition and a frightening path to electoral relevance. One early ballot confirmed him with about 3 p.c help. However because the weeks glided by, he shot up within the polls, introducing himself to voters with 15-second TV spots and stunning opponents who centered their early assault strains on better-known candidates.

Mr. Johnson, 46, who’s Black, got here in second in a primary spherical of balloting final month. He carried out particularly effectively in liberal, principally white wards alongside the town’s northern lakefront and in areas northwest of downtown with giant Hispanic populations. Mr. Vallas, 69, who’s white, got here in first place, working up giant margins round downtown and in addition carrying majority-white areas on the Northwest and Southwest Sides.

Mr. Johnson’s speedy ascent was fueled by his present for retail politics, a message that resonated with the town’s sizable bloc of liberal voters and huge donations from labor unions. State information present that of the greater than $5.6 million in contributions Mr. Johnson’s marketing campaign reported between the beginning of 2022 and earlier this month, greater than $5.2 million got here from organized labor, together with vital sums from the Chicago Lecturers Union, the American Federation of Lecturers, the Illinois Federation of Lecturers and branches of the Service Workers Worldwide Union. Since final fall, the Chicago Lecturers Union and its political motion committee have contributed greater than $1 million to the Johnson marketing campaign.

Stacy Davis Gates, the president of the Chicago Lecturers Union, which has greater than 20,000 members, stated there was no expectation that Mr. Johnson could be in lock step with the union if elected. However she stated the potential of having a mayor who understood the struggles of classroom educators and would take heed to their considerations had motivated academics to help him.

“It’s been troublesome for my members over the course of those few years,” stated Ms. Davis Gates, whose union engaged in work stoppages in 2012, 2019 and, after a dispute with Mayor Lori Lightfoot over Covid-19 protocols, once more in 2022. “They haven’t been revered or handled because the stakeholder that they’re on this metropolis,” Ms. Davis Gates added. “They’re on the lookout for partnership.”

Mr. Johnson’s shut ties to the academics’ union could be useful: Liberal politicians covet the union’s endorsement, and in a 2019 ballot reported by The Chicago Solar-Occasions, 62 p.c of voters stated they’d a positive opinion of C.T.U.

However amongst Vallas supporters, Mr. Johnson’s C.T.U. ties have turn out to be a degree of criticism. As a C.T.U. member and organizer, Mr. Johnson helped the union exert its affect and problem the mayor on a number of points.

“He’s going to do what the union desires to be executed,” stated Gery Chico, who led Chicago’s college board when Mr. Vallas was the chief govt of Chicago Public Colleges, and who has endorsed Mr. Vallas for mayor.

Because the C.T.U.’s political affect has grown during the last 12 years — first as a chief antagonist of Mayor Rahm Emanuel, who oversaw college closures, then with Ms. Lightfoot, who fought with the union about work circumstances and Covid reopenings — some have questioned its function in Chicago politics. In an interview in 2021, Ms. Lightfoot recommended that each the C.T.U. and the native chapter of the Fraternal Order of Police, which has endorsed Mr. Vallas and whose leaders usually help Republicans, had moved past the normal function of labor unions and turn out to be extra overtly political, creating inevitable battle.

Mr. Johnson, the son of a pastor, plans to finish his membership within the academics’ union if elected mayor. When requested whether or not there have been areas the place he anticipated to have to inform the union no, Mr. Johnson didn’t present particular examples.

If elected mayor, “my duty is to your complete metropolis of Chicago,” he stated. “And look, I’m getting new mates each single day. And I’ve a bunch of outdated mates that we must have laborious conversations with.”

Mr. Vallas has repeatedly criticized the C.T.U. and tied Mr. Johnson to the union’s reluctance to return to in-person instruction through the pandemic.

“Brandon was partly chargeable for the shutting down of one of many poorest college programs within the nation, with devastating penalties,” Mr. Vallas stated throughout a latest debate, including that “for those who take a look at the crime statistics, and also you take a look at the violence, and also you take a look at the dislocation and declining check scores, you may see the outcomes.”

In the course of the marketing campaign, Mr. Johnson has described a Chicago dogged by inequality, affected by violence and constrained by colleges that lack the sources they want. That worldview, he stated, was formed by his time in Room 309 of Jenner Academy in Cabrini-Inexperienced, the place he taught from 2007 to 2010, a time when lots of his college students’ houses had been being demolished as a part of a citywide push to knock down public housing high-rises.

“The kids had been waking as much as bulldozers — actually simply bulldozers watching us all day lengthy,” Mr. Johnson stated in an interview in Selma, Ala., the place he traveled this month as a visitor of the Rev. Jesse Jackson for the annual commemoration of Bloody Sunday. “And there have been households the place their houses had already been dismantled, so we had college students who had been taking two buses and a practice to return again to the varsity.”

In Cabrini-Inexperienced, former colleagues stated, Mr. Johnson was a uncommon Black male trainer at a college the place virtually the entire college students had been Black. He revived defunct basketball and flag soccer groups, gaining a popularity as a nurturing coach with a aggressive streak. And he was often known as an enticing however demanding trainer who requested college students to decorate up on days once they gave a presentation.

“The self-discipline that he confirmed and the love that he confirmed for the youngsters, the youngsters revered him,” stated Pat Wade, a college safety officer and coach who labored with Mr. Johnson in Cabrini-Inexperienced. “They usually labored laborious due to what he gave to them. Lots of people can’t do this.”

Mr. Jackson, a Chicagoan who has endorsed Mr. Johnson’s bid for mayor, emphasised the candidate’s report of working with kids in a metropolis the place many younger individuals lack alternative and are caught up within the legal justice system.

“These troubled youth in Chicago,” Mr. Jackson stated, “he represents a face of hope for them.”

However Mr. Johnson has confronted criticism for his views on crime, the largest difficulty within the marketing campaign. In 2020, he described defunding the police as a political purpose and supported a County Board decision to “redirect funds from policing and incarceration to public companies not administered by regulation enforcement.”

As a candidate, Mr. Johnson has tried to distance himself from questions on defunding, and he has known as for hiring extra police detectives in addition to elevated funding for psychological well being companies.

Mr. Johnson stated he noticed similarities between the criticisms he has confronted on policing and people leveled in opposition to Harold Washington, Chicago’s first Black mayor, 40 years in the past.

“This isn’t new to the town of Chicago: Yet one more assault on a Black man as an elected chief who’s dedicated to investing in individuals,” Mr. Johnson stated.

However simply as his ties to the academics’ union have been seized on by his political opponents, skepticism about Mr. Vallas’s endorsement from the police union may present a gap for Mr. Johnson.

Scott Lewis, a North Aspect resident, stated he agreed with Mr. Vallas that crime was uncontrolled. However he nonetheless deliberate to vote for Mr. Johnson.

“In comparison with the others, he appears slightly too cozy with the F.O.P. for my style,” Mr. Lewis stated of Mr. Vallas. “The police do have an essential function, however I believe reform is essential.”

Robert Chiarito contributed reporting from Chicago. Matthew Rosenberg additionally contributed reporting.