When Chicago’s mayor, Rahm Emanuel, was recently in New York to appear on Stephen Colbert’s late-night television show, Colbert asked how he would enforce his declaration that Chicago was now a “Trump-free zone.” “The whole thing? How does that work?” Colbert asked. Yes, Emanuel replied, nodding his head vigorously, “The whole thing. Our motto: a city he’ll never sleep in. We don’t want him, man.” At that, he smiled broadly as the audience cheered.

Of course, Emanuel can’t actually bar the President of the United States from entering America’s third-largest city. But the loud applause that followed his comments reinforced a key fact of politics in 2018: if you’re a Democratic mayor in a Democratic city, Trump-bashing is good for business. And Emanuel, who has revelled in political brawls since he was a young enforcer in Bill Clinton’s White House, has taken to it with even more vigor than most. Trump, the Mayor told me when we met last week in his office at Chicago’s City Hall, had made the fight personal, and Emanuel said that he is happy to oblige. “I’m not scared, I’m not intimidated, so I’ll say it, and he gets irritated, so he thinks he can hit me in the nose,” Emanuel said. “The city of Chicago, we’re the city of big shoulders—we’ll hit back.”

The President has long appeared to be obsessed with Emanuel’s Chicago, portraying it as a sort of murderous hellscape, a symbol of the “American carnage” that he vowed to eradicate in his Inaugural Address. Trump has called Chicago “a disaster,” “out of control,” and “Not Good!” On the campaign trail, in 2016, he regularly cited the city’s high murder rate and even claimed to have met with a high-ranking Chicago police official who said that he could fix the city’s problems “in one week” if only he and his men were unleashed. Since becoming President, Trump has continued to single out Chicago as a dangerous urban cesspool. “What the hell is going on in Chicago?” Trump shouted at a campaign-style rally in Pensacola, Florida, in December. A few days later, Emanuel issued his televised vow to ban Trump from Chicago. And a few days after that, Trump had the city on his mind once again. “What the hell is going on in Chicago?” he asked the graduates at the F.B.I. Academy, in Quantico, Virginia, in what was, even for Trump, a most unusual digression during a commencement address. “What the hell is happening there?”

A feud between these two almost theatrically combative politicians was perhaps inevitable. Both love a fight, and both believe that if you are punched in politics, the only correct course is to punch back. And this fight is mutually beneficial. For Trump, the portrayal of the city as a gigantic crime scene filled with rogue immigrants and gun-wielding murderers seems tailor-made to appeal to his political base of disaffected white voters across the Rust Belt suburbs and exurbs. For Emanuel, the benefits of a fight are equally appealing. As the 2016 election season closed, the former Washington wunderkind, who had gone on to become Barack Obama’s first White House chief of staff, was a struggling second-term mayor with low approval ratings. Racial politics in the city had turned even more toxic than usual after evidence emerged of police misconduct in the death of a seventeen-year-old African-American named Laquan McDonald. Many questioned whether Emanuel could run for or win a third term.

Then came Trump. In the Presidential election, the blustery New Yorker won just twelve per cent of the city’s popular vote and fifty-one of Chicago’s two thousand and sixty-nine precincts. Hating on Trump was something that Emanuel’s bitterly divided city could agree on, and the Mayor embraced his new role. Suddenly, he was in demand again on the national talk-show circuit; he wrote op-eds for the Washington Post and the Times and joined his fellow-big-city mayors in filing lawsuits against Trump’s immigration policies. By the end of December, after his “Trump-free zone” line had taken off, Emanuel’s approval rating had gone up from an abysmal twenty-five per cent to well over fifty per cent.

How much did Trump have to do with Emanuel’s resurgence in Chicago? It’s hard to say, of course, but Emanuel is taking advantage of the political lift. He announced that he plans to run for a third term next year, and there are no serious challengers yet on the horizon. When we met in his City Hall office on a bone-chillingly cold afternoon last week, Emanuel acknowledged that his blunt criticism of Trump is popular in a place where public sentiment leans hard against the President. “The good news is, the city has stood up and said very particularly to him his politics and his policies are not welcome here,” he said. “And I’m just giving voice to what people already feel.”

Emanuel told me that the “Trump-free zone” line went back to an impromptu moment at the beginning of the past school year. He was visiting a predominantly Hispanic high school (“as in ninety-nine-point-nine per cent Hispanic,” he said) on the southwest side of Chicago, where fears were running high about deportations and Trump’s plans to cancel the legal status for the young people, known as Dreamers, who had been brought to the United States illegally as children. “I wanted their parents and them to know they belong in school, they’re going to be safe in school, they’re going to be safe going to and from school,” he said.

I asked Emanuel why the President seemed so obsessed with Chicago. “I don’t think he likes the fact that I’m pretty vocal. I’ve been in the Oval Office; I’m not intimidated by it. I worked for two Presidents that weren’t scared when I tell them I disagreed. They encouraged me to speak my mind,” he said, drawing a quick contrast with congressional Republicans back in his old stomping ground on Capitol Hill. “Look at the House Republican caucus—he prefers a bunch of lemmings.” When I laughed, Emanuel said, “Well, he does! You have a very, very autocratic personality. He doesn’t like things that are in his way.”

Hating on Trump, while it may be fun, has its limits. If anything, the ease of Trump-bashing, the daily chaos of his Presidential Administration, and the many rifts now playing out in public among Republicans have obscured the equally tectonic fight going on inside the Democratic Party. Since the unexpected success of Bernie Sanders’s 2016 insurgency against Hillary Clinton, the Party has been conflicted between its increasingly loud left wing and its governing center.

Emanuel is acutely aware of this. “To quote Bill Clinton,” he said, breaking into a well-honed impression of the former President, “you can’t beat something with nothin’. We’ve established we’re against Trump. I want to establish we’re for America.”

Emanuel has always stood for a certain Clintonian centrism, even though that brand of nineties-style pragmatism has since gone out of fashion in the Democratic Party. “Democrats can keep winning: Just copy (Bill) Clinton” was the title, in fact, of an article he published with another former Clinton White House aide, Bruce Reed, in the Washington Post, in November, as Democrats scored off-year election victories in New Jersey and Virginia and looked ahead to this year’s midterm elections. Their argument was simple: win the war of ideas against Republicans, and aim for a majority rather than playing to the Democratic Party’s existing liberal base. But it is not a fight they are winning, as the pair readily acknowledged in the piece. “Instead of reaching out to the nearly 60 percent of Americans who disapprove of the president and may be looking for a new political home, Democrats are once again fighting over whether to purge one wing or frustrate the other,” they wrote.