If you like your political campaigns bloody, then you have to be cheered by the new poll that found Chicago Teachers Union president Karen Lewis beating Chicago Mayor Rahm Emanuel in a hypothetical matchup 45 to 36. Lewis, who’s been Emanuel’s primary political antagonist for the last three years and led the 2012 teacher’s strike that represented the first chink in Emanuel’s mayoral armor, had long said she had no interest in running against him next February. But in recent weeks, as Chicago (and Emanuel) have reeled from yet another outbreak of gun violence, she began to soften that stance. And when Chicago Sun-Times reporter Natasha Korecki informed Lewis over the weekend of the poll results that found her beating Emanuel by 9, Lewis’s response sounded like that of someone who’d just been pushed off the fence. “Wow,” she said. “Well, first of all, I’m sitting here stunned.”

Lewis is rarely at a loss for words—especially when it comes to Emanuel. The two have clashed from the beginning of their relationship. Shortly after his election in 2011, Emanuel invited Lewis to dinner at a fancy French restaurant across from Millennium Park. There, according to Lewis, he told her in between bites of lamb that, owing to budget constraints, he did not want to waste precious resources on the bottom 25 percent of Chicago public school students. At a meeting in his City Hall office a few months later, Lewis says, she was arguing with Emanuel over his proposed longer school day when he erupted, “Fuck you, Lewis!” (Emanuel has heatedly denied the former charge by Lewis about writing off the bottom quarter of public students and essentially pled nolo contendere to the latter about his bad language.) In the run-up to the strike, Lewis called Emanuel “a liar and a bully.” On another occasion she branded him “the murder mayor,” elaborating: “Look at the murder rate in this city. He’s murdering schools. He’s murdering jobs. He’s murdering housing.”

“I just think there’s something clearly wrong with him,” Lewis told me last year when I sat down with her at CTU’s offices in the Merchandise Mart. A heavyset African-American woman in her early 60s, Lewis was a Chicago public school chemistry teacher for 25 years before she was elected CTU president in 2010. Although they might seem polar opposites, she and Emanuel have a lot in common. Both are former dancers and ballet aficionados, as well as products of elite colleges: Lewis was the first African-American woman to graduate from Dartmouth; Emanuel attended Sarah Lawrence. And Lewis, like Emanuel, is Jewish, having converted from Lutheranism 20 years ago. (She did not invite Emanuel to her Bat Mitzvah last summer.)

Their greatest similarity is their temperaments. When Emanuel cursed her at City Hall, Lewis told me, her immediate thought was: “Who the fuck do you think you’re talking to? I’m from the South Side, bitch.” But she swallowed her tongue and later played the episode for public sympathy. “He managed to make Karen Lewis, who’s anyone’s idea of a media rock star, into a positive figure,” one Emanuel ally lamented to me. And Lewis has continued to outmaneuver the mayor. When Emanuel’s school board moved to shutter 50 schools, it was Lewis who, seizing on the fact that most of the condemned schools were in African-American neighborhoods, led the demonstrations outside City Hall at which protestors chanted, “Hey Rahm, let's face it, these closings are racist!”

Indeed, the biggest reason Emanuel is in such political trouble right now is because of his unpopularity with Chicago’s black voters. When Emanuel ran for mayor in 2011, fresh off his stint as White House chief of staff, he wore what Lewis calls “the Obama halo” and won 59 percent of the city’s black vote. But his battles with the teacher’s union and Chicago’s horrible gun violence (which has disproportionately impacted the city’s black neighborhoods) have taken a huge toll on his African-American support. A Chicago Tribune poll from last year found that 48 percent of African-American voters disapproved of his performance as mayor. And in the new Chicago Sun-Times poll that found Lewis beating Emanuel by 9 points overall, she bested him by 18 points among black voters.