Within seconds of stepping onstage to declare his triumph in the Chicago mayoral race, Brandon Johnson extended an olive branch.

After briefly marveling at his improbable political rise, the newly minted mayor-elect said his first order of business was delivering a message to those who’d voted for his opponent, Paul Vallas.

“I want to work with you, and I’ll be the mayor for you too,” Johnson said, after the audience’s light grumbling over the mention of his rival.

But bringing the city together after the bitter race may be even more improbable, given the cavernous differences between Johnson, who will enter City Hall as one of America’s most progressive big-city mayors in generations, and his more conservative rival who ran a law-and-order campaign.

Unofficial results showed voters were deeply divided, with Johnson winning 51.7% and Vallas 48.3%. Though tens of thousands of mail-in ballots remain to be tallied, geographical and racial fissures are already evident.

In an interview with the Tribune, Johnson said he will try to focus on issues where there’s room for consensus.

His 100-day agenda: doubling the amount of youth workers, finalizing a “Treatment Not Trauma” plan to send a non-police response to certain mental health crises and passing “Bring Chicago Home,” a plan to hike the real estate transfer tax on properties above $1 million to fund anti-homelessness initiatives.

In a later appearance with Illinois Gov. J.B. Pritzker, Johnson was less bullish on whether he could pass the last initiative in that time frame, given that it requires a change in state law.

He also plans to focus on environmental issues.

“I talk about Austin a lot. Austin is beautiful. It is also a hot spot when it comes to environmental injustice, right?” said Johnson, the city’s first West Side mayor in almost a century.

To start, Johnson wants to commission a “cumulative impact study,” which will segue into rebuilding a fully staffed Department of Environment, which was dismantled by former Mayor Rahm Emanuel and never brought back under his successor, Mayor Lori Lightfoot, despite her campaign promises to do so.

This would all serve to “unite the city” around the theme of “environmental justice,” Johnson said.

“Obviously, I have some spaces — the Southeast, Southwest Side of Chicago — that are top of mind, but of course, West Side. You look at Roseland and Englewood, there’s some real environmental dynamics there that are quite harmful,” Johnson said.

He acknowledged big questions around how he will turn campaign pledges into realities.

After speaking broadly about what he sees as his mandate to tackle public safety via investments in mental health care and jobs for young people, he quipped: “Now, I know you’re going to ask me how we pay for it. But we’ll get to that. I’m sure we’ll get to that. So those are the things that we agree on.”

On the campaign trail, Johnson did tout a bundle of tax hikes that were a frequent source of criticism from Vallas, however. Beyond the Bring Chicago Home proposal, Johnson’s ideas to raise about $800 million in revenue include a head tax on Chicago employers and a jet fuel tax, as well a hotel tax increase. But Pritzker also cast doubt on another Johnson initiative that would require state legislative action: a levy on financial transactions.

In one postelection cable TV appearance, Johnson also repeated a promise to not raise property taxes.

Perhaps the most crucial decision Johnson faces early in his term is who he selects as police superintendent. Lightfoot’s choice, David Brown, was blamed for much of the low morale and churn among the rank-and-file, and both mayoral runoff candidates had pledged to fire him — before he departed on his own last month.

The nascent Community Commission for Public Safety and Accountability is in the process of culling feedback and names. Potential candidates include former chief and West Sider Ernest Cato III, who was a 2020 finalist for the top job that went to Brown; South Sider and Deputy Chief Larry Snelling; and Angel Novalez, the Police Department’s current head of reform.

On the search, Johnson said, “I want to make sure that law enforcement, of course, is at the table, (plus) the faith community, the business community and people impacted by violence.” He also noted that he has the support of more than half of the newly elected police district council members.

“I’m confident we’ll come up with a process that will be transparent, that brings real co-governance to the city of Chicago, because I believe that actually helps unite the city as well,” Johnson said.

He acknowledged the historic “tension and some rub” in the police’s relationships with many constituents. But he also stressed that those same communities, though wary, do not want to see “our systems break down.”

“We have to be honest about it,” Johnson said. “Even Paul Vallas recognizes that there are tensions there, that I’m going to be a mayor that’s intentional about making sure that the conversation is not just had but we come to an agreement of how we address those tensions.”

Though Johnson’s victory is being hailed as a watershed endorsement of the progressive movement and his campaign message of ending the “tale of two cities,” the vote breakdown showed a deeply split electorate.

Perhaps it’s no surprise that a match-off would be close between two candidates who hailed from opposite extremes in the original nine-candidate field, a feature that contributed to them advancing to the runoff over more moderate choices.

The race was also between two Chicagoans who, despite both labeling themselves Democrats, came from starkly different political spheres and frequently engaged in dust-ups that got personal.

To hear Vallas tell it on the debate stage and in attack ads, Johnson was from the radical wing of the party, and his past rhetoric in support of the “defund the police” movement would further degrade law enforcement. Meanwhile, Vallas would have been a “privatizer-in-chief” eager to cripple public schools, in Johnson’s previous words.

Vallas seemed to grasp the enmity between their camps too, and he took pains in his concession speech to quiet boos from the crowd of his supporters — some of whom seemed to hope he would fight the results — before saying Johnson has his full support as the next mayor.

Johnson largely won the Black vote that had gone to Lightfoot in February’s first-round election, suggesting Vallas’ firewall of endorsements from African American establishment politicians, as well as their arguments that those in the city’s most violent tracts want more traditional policing, had faltered.

Among the 14 majority-Latino wards, Johnson won those encompassing Chicago’s most storied Mexican American and Puerto Rican enclaves: Little Village, Pilsen and Humboldt Park. But Vallas still held on to eight, though some by slim margins, unofficial results as of Friday afternoon showed.

While Vallas won the sole, new majority-Asian ward, white-majority or -plurality wards were split. Both candidates held onto their bases: Johnson’s Milwaukee Avenue progressives and Vallas’ bungalow belt conservatives.

Meanwhile, Vallas’ strongest support along the north lakefront began downtown, but his share of the vote slipped the farther north the wards were, with Johnson winning north of the border between Lincoln Park and Lakeview.

Ron Rymarczyk, 61, a South Loop and retired IT professional, voted for Vallas and was disappointed by the outcome, especially because the race was “pretty tight, and not a lot of people voted, which makes it worse.”

Johnson “said he’s going to unite everybody, and I really hope he does,” Rymarczyk said. “He made some comments in the past that were the reason I didn’t vote for him as far as defunding the police and taxing big business. I’m just afraid he’s going to milk everybody dry. That’s not what we need.”

McKinley Park resident and stay-at-home mom Lydia Arroyo, 45, said she supports Johnson and that “the only way he’s going to convince (doubters) is by proving the changes that he can bring about and showing that he can get the city under control.

“I liked the message he was giving, basically trying to unite the city,” Arroyo continued. “There is a lot of division. People are worried about violence. I am myself. I understand where people are coming from, but I think it’s a multifaceted problem and it’s going to need more than just adding more officers to the street.”

Beyond unifying the city, there’s a question of whether Johnson can even unite a fractious City Council. That will depend on his approach, say aldermen who endorsed Vallas and whose wards voted for Vallas.

“I don’t think he has a choice other than to unite,” said Ald. Anthony Napolitano, 41st, a former police officer and firefighter whose ward covers the city’s Far Northwest Side and O’Hare Airport. It’s a tough assignment, since “more than I’ve ever seen going on in my 24 years working with the city, I’ve never seen a City Council so divided and separated and angry at each other.”

Even so, Johnson has a model of how not to engage the council, courtesy of his predecessor, Napolitano said.

Johnson “can look at (Lightfoot’s) blueprint and say, ‘Wow, this didn’t work at all.’ One of the biggest problems in council was the mayor didn’t communicate with council members. She picked fights, she held grudges,” Napolitano said. “When (Emanuel) had an issue or situation and he wanted your support for it, if you didn’t support him, he was so mad at you at that point, but when that point was over, he was back to business and started fresh on every single topic. I thought the world of that.”

Ald. Raymond Lopez, 15th, a frequent Lightfoot foe who backed Vallas, has expressed worry about the council’s leftward shift, including the five socialists recently awarded key committee chairmanships.

“I would not be surprised if the new mayor, working with his fellow socialists and uber-left aldermanic allies, (does) not try to reorganize the chairmanship and structure and council in a way that is more conducive to their political needs,” he said.

Johnson “will have the same choice Lori Lightfoot had,” Lopez added. “You either use this moment and move forward, or you return to the politics of being petty and vindictive and continue the turmoil that’s existed from one administration into the next. This is his moment. How he chooses to use it will be up to him.”