The Chicago Teachers Union’s (CTU) internal election is this week. Internal union elections don’t usually draw much attention, but this one is important: the incumbent slate is the Caucus of Rank-and-File Educators (CORE). CORE is the caucus of former CTU president Karen Lewis and other left militants who took over the leadership in 2010 promising to remake it into a fighting force. In 2012, CORE took the CTU into a major strike that made the union the most powerful workers’ institution in the city.

That transformation has had detractors. CORE, whose slate is headed by current union president Jesse Sharkey and Vice President Stacy Davis Gates, is up against a slate called Members First (MF), which argues against CORE’s style of militant unionism on behalf of the city’s entire working class in favor of a more conservative, bread-and-butter unionism.

Those who want working-class power in Chicago and militant teachers unionism across the country to keep growing should hope for a CORE victory on May 17. To understand why, we can take stock of CORE’s achievements in office.

Most important is the CTU’s 2012 strike. During the “red state revolt” that saw teachers strikes sweep through much of the country last year, then the “blue-state revolt” that took off this year, many commentators seemed to forget that it was Chicago that first put teacher militancy back on the national agenda. That strike was the product of a reborn CTU under CORE, which educated and activated its members in new ways, slashed union staff salaries, made organizing alongside parent and community groups central, and waged a successful walkout.

The union’s seven-day 2012 strike — which included an incredible two extra days for rank-and-file teachers to examine the union contract on their own before deciding to go back to school — was a rare victory in recent American labor history, the most important by any union in at least a decade and a half. What was so notable about the strike wasn’t just its highly democratic, militant character, but that it was very explicitly a strike on behalf of the city’s entire working class.

The union constantly argued it was fighting for “the schools Chicago’s students deserve” and made a working-class antiracism central to their organizing, contrasting their own approach to the one advanced by billionaire-backed charter school boosters. Citing the brutal impact of austerity in education and beyond on the city’s neighborhoods of color — what the union called “educational apartheid” — they won strong support from the city’s black and Latino public-school parents, even in the midst of the strike. That support has stayed strong in the years since.

After decades of a severed relationship between teachers unions and parents and community members of color, the CTU rebuilt that coalition. In their strikes this year, teachers unions in cities like Los Angeles and Oakland have followed in Chicago’s footsteps.

Shortly after the strike, the union mobilized against Emanuel’s closure of forty-nine schools throughout the city, mostly in poor and working-class, black and Latino neighborhoods. The CTU lost that fight, as Emanuel’s handpicked school board approved all of the closures. But the mayor paid an enormous political price.

The closures and fightback against them helped cement the narrative that “Mayor 1 Percent” cared little for the city’s working class and helped lead to his downfall, forming the backdrop for the Laquan McDonald scandal, in which Emanuel’s office helped helped cover up a Chicago police officer’s murder of a black teenager in a hail of sixteen bullets (over which the CTU joined calls for Emanuel to resign). After years of being hammered by the CTU for not caring about the city’s working-class neighborhoods (Karen Lewis famously called Emanuel “the murder mayor”), the revelation that his office had covered up an actual police murder was the nail in the coffin of his time as mayor.

The union has also repeatedly gone after the ultra-wealthy to pay for what the city needs. They have repeatedly attacked the city’s tax increment financing (TIF) program, which often serves as an undemocratic giveaway to real-estate developers, luxury hotels, financial institutions, and other wealthy corporations. Their 2016 illegal, one-day strike was explicitly over increasing revenue — in other words, taxing the rich.

At a January press conference, union Vice President Stacy Davis Gates explained — in the kind of succinct language that should be a model for unionists and left activists around the country — how to fund the union’s next contract demands: “Where would the money come from? Rich people.”

Since the strike, the union has become the anchor of the left wing of the city’s politics, along with a number of other progressive unions and community groups: the union and its allies have been on one side, Mayor Rahm Emanuel and the city’s ultra-wealthy (and, it should be noted, more than a few opportunistic unions) on the other. The CTU is the principal funder of United Working Families, the union-community political organization which has funded a number of left candidates on Chicago’s city council, including all six of the Democratic Socialists of America members that recently won.

And the union has carried out what is far and away the most aggressive, most successful charter-school organizing drive in the country, with four different charter schools going on strike in Chicago in the past six months. Those strikes led to wage parity with the Chicago Public Schools contract (undermining charters’ ability to undercut neighborhood public schools’ labor costs, a key reason education privatizers push charter schools in the first place), class size reductions, and guaranteed staffing of social workers and other wraparound services for students. The strike at Instituto charters produced a 40 percent (!) wage gain over the next two and a half years.

Their model has spread to teachers unions around the country through UCORE, a network of rank-and-file teacher activists looking to push their unions in a more militant, democratic direction. And the CTU model has been a beacon for teachers in the current strike wave.

Eric Blanc recounts in his new book Red State Revolt how teacher militants in West Virginia studied my book on the 2012 strike Strike for America, Labor Notes’ book How to Jump-start Your Union, and Jane McAlevey’s No Shortcuts, which includes a chapter on the CTU, as they prepared for their 2018 strike. Blanc also recounts the importance of Arizona teacher Rebecca Garelli in last year’s strike there; Garelli was a teacher in Chicago during the 2012 strike and repeatedly drew on lessons from that experience in organizing the strike in Arizona.

In short, without CORE, it’s unlikely that much of the working-class gains made in Chicago in recent years would have ever come to fruition, and the national upsurge in teacher militancy would have been without a key model to draw from.

As with any group of leaders, CORE’s record hasn’t been flawless. Some members, including those who identify as leftists, aren’t happy about the union’s decision not to strike in 2016 beyond a one-day strike in April, or the CTU’s strong backing of Toni Preckwinkle in the recent mayoral election, who lost to corporate attorney Lori Lightfoot by massive numbers. Many have been frustrated that the union has not been able to stop round after round of cuts in the district, making teaching conditions worse and worse — a situation beyond the leadership’s control, but maddening nonetheless.

Still, CORE has made the CTU into one of the most important teachers union locals in the country, a model of militant unionism that has won the support of the majority’s of the city’s working class by advocating an agenda for the city’s whole working class. And their opponents in the race want to roll that model back.

Like many other cities around the country, Chicago has been ravaged by austerity in recent years. But unlike most of them, a strong working-class movement has actually begun to fight back and win. The CTU, led by the CORE caucus, is central to that movement; CORE’s reelection is needed to keep building that movement.