New York State has voted for every Democratic presidential nominee since 1988, usually by an overwhelming margin. The State Assembly reflects that political proclivity with consistent Democratic majorities. But with the exception of one brief interregnum in 2009, the upper chamber—the State Senate—has remained firmly under Republican control. There are numerous reasons for this disconnect—from incumbent protection rackets to rampant corruption in the state capital—but in recent years, the key actors in this power play have been a group of Democrats called the Independent Democratic Conference (IDC), and New York’s two-term Governor, Andrew Cuomo.

Elected as a Democrat to his first gubernatorial term in 2010, Cuomo quickly acquiesced to an electoral map drawn by (and designed to favor) the New York State GOP. Despite that partisan gerrymander, New York Democrats still managed to claw together a narrow Senate majority in 2012—but that victory was instantly thwarted by four nominally Democratic state Senators who, calling themselves “Independent Democrats,” joined in a power-sharing agreement with the minority to keep control of the State Senate in Republican hands. All of this was done with the tacit approval (and many would say the active engagement) of Cuomo. The IDC members were rewarded with powerful committee seats and “lulus” (New York legislative slang for bonuses doled out to lawmakers in leadership), and Cuomo was able to use a divided legislature as a convenient excuse for his political vicissitudes. At different junctures, the IDC has announced its dissolution (often with the governor taking credit for uniting the party), only to see it return—usually after an election, sometimes with more members, and always firmly allied with Republicans.

For years, this was, unfortunately, seen as largely uncontroversial in New York politics, and (equally as unfortunate and not unrelated) under-covered by the media. But with a blue wave building ahead of the November elections, it’s looking likely that the movement that delivered a primary victory to Alexandria Ocasio-Cortez over a high-ranking Democratic incumbent in a US House race earlier this summer will crest again in September. And that wave has the potential to wipe out a quarter of the state’s incumbent Democratic caucus. Led by women and the emergent progressive movement, 10 Democrats in the New York State Senate face primary challenges (eight IDC members, one Democrat who outright caucuses with Republicans, and one centrist mainline Democrat), of which at least half are likely to be successful.

And, given the partisan makeup of New York’s electorate, once Democrats take real control of the State Senate, the GOP would have difficulty winning it back. At a time when states could lead the fight against Trumpism, this makes New York’s upper chamber one of the most important battlefields of this election cycle. Still, as the newly engaged progressive base of the Democratic Party looks to make big changes nationally—first fighting Trumpism, then advocating for a more progressive social order—New York’s politics lag behind. And that is mostly due to the efforts of the Independent Democratic Conference.

The relationship is confusing because, in many instances, IDC members signal support for progressive legislation. But, this support is meaningless when Republican control of the chamber prevents progressive legislation from ever receiving a vote. By handing control of the State Senate to Republicans, the IDC killed a state version of the Dream Act, which would have helped undocumented youth attend college, and it blocked action on legislation involving affordable housing, expanded voter registration, a comprehensive green-energy plan, a gender expression nondiscrimination act, single-payer health insurance, and a constitutional amendment guaranteeing women’s reproductive rights. All of these passed the Democratic-controlled State Assembly with ease, but couldn’t get through the Senate because IDC members had ensured Republican control of the chamber.

Now, a slate of candidates is running on a platform of passing the Assembly’s Democratic agenda through the State Senate. From the New York Health Act (a state single-payer insurance plan) to a green jobs bill, from universal rent control to a universal-basic-income pilot project, these candidates campaign for the things progressives across the country want to see on legislative dockets.

The first candidate to jump into the fray was activist and former New York City council member Robert Jackson, who faced Marisol Alcantara in 2016 for the Democratic nomination in the 31st district, a deep-blue constituency on Manhattan’s west side. Boasting progressive values, Alcantara won a plurality when Jackson and a third candidate split the anti-IDC vote—but upon reaching the State Senate, Alcantara immediately joined the IDC. This cycle, with the opposition consolidated behind him, Jackson is challenging Alcantara again.

In January, Jessica Ramos, a former de Blasio aide and Democratic district leader, announced she was taking on Senator Jose Peralta in the 13th, an ethnically diverse district in Queens. Peralta, already weakened by his association with the IDC, became weaker when he appeared in public with disgraced former state senator and convicted domestic abuser Hiram Monserrate, and weaker still when the head of the Queens Democratic machine, Representative Joseph Crowley, lost his US House primary to Ocasio-Cortez (activists relay stories of seeing Peralta’s face drop at learning of Crowley’s concession).

Ramos’s decision was not easy—she has two small children and running for office meant giving up a well-paying job at a time when it was far from certain how much backlash the IDC would engender. But in the end, the betrayal she felt watching Peralta trade promises to defend the district’s large immigrant community for those shady lulus offered by the Independent Democrats propelled Ramos to launch a bid. “As a public-school mom, a renter, and the daughter of immigrants, I’ve watched my community suffer because of Jose Peralta’s alliance with the Senate Republicans,” Ramos told me. “I knew I had to stand up for my family and my neighbors and say: enough.”

Progressive Zellnor Myrie has been working for nearly a year (he announced last October) to unseat Senator Jesse Hamilton, who conferences with Republicans despite representing a district (the 20th) that Hillary Clinton won with more than 90 percent of the vote in 2016. Myrie has focused his campaign on housing affordability, and has rolled out a plan for aggressive rent regulation. Hamilton, the incumbent, has been feeling the heat—when asked about his alliance with the IDC, he referred to the idea that they empower Republicans as “fake news” (a Trumpian turn of phrase the community noticed). Hamilton also lost the backing of an influential Democratic club when he walked out on an endorsement meeting rather than answer probing questions on his housing plan. The group endorsed Myrie instead, and most of the Democratic power structure in the district soon followed suit.

Alessandra Biaggi has raised the most of any anti-IDC challenger. Biaggi is running to unseat Jeff Klein—the leader of the Independent Democratic Conference for seven years. Klein has long been seen as invulnerable in his district, but cracks have emerged. Earlier this year, he was accused by a former staffer of sexual misconduct. Further, Klein is relying on the same ailing machine as Crowley. Meanwhile, Biaggi has name recognition due to her popular grandfather, Mario. (A highly decorated New York City police officer and 10-term member of Congress, the elder Biaggi was forced to resign his House seat in 1988 because of financial corruption. Mario died in 2015.) Alessandra has picked up endorsements from the powerful service-workers union local 32BJ, and from Ocasio-Cortez. Biaggi also was endorsed by Corey Johnson, speaker of the New York City Council, prompting Klein to accuse her of “parading” around Manhattan with Johnson— a dog whistle the openly gay, HIV-positive speaker criticized.

Activist Jasmine Robinson is running against incumbent IDC senator Diane Savino in Staten Island. Robinson was active in Black Lives Matter and has grown increasingly frustrated by the lack of attention the State Senate and IDC were paying to activist movements. “I witnessed the sadness of a community who feels that they are taken for granted,” she told me, “I wanted to let all neglected communities know I am in this race for them. I recognize your pain because it is the same as mine.”

Syracuse University administrator Rachel May is campaigning on single-payer health insurance against Democrat David Valesky, who worked with the GOP to block it. Librarian Julie Goldberg is challenging Sen. David Carlucci in the 38th, a district in Rockland and Westchester Counties. And most recently, John Liu formally entered the race against IDC-allied senator from Queens Tony Avella. (Liu came within 900 votes of unseating Avella in 2014, and this time out quickly won an endorsement from Council Speaker Johnson.) With Liu on the ballot, every incumbent IDC member will have a well-organized challenger.

Liu’s bid speaks to the way that the resistance is changing the party. He recruited two prominent, progressive women for his staff: Heather Stewart from Empire State Indivisible (the New York chapter of the national resistance movement) to be his communications director, and Lisa DellAquila from True Blue New York (a group formed to oppose the IDC) as his campaign manager. Stewart told me that Liu “understands that women are making a move and that having women run the campaign would bolster that energy.”

Most of the candidates haven’t run for elected office before (Liu and Jackson are the exceptions), and their candidacies have an authenticity that many aspirants struggle to replicate. Lauren Goldenberg, a resident of Myrie’s district, told me about how she and a friend were hosting a postcard-writing session in Crown Heights. On a whim, they direct messaged the candidate on Twitter. He didn’t message back, but shortly after, he stopped by the event, grabbed a beer, and gave an impromptu talk to the gathered attendees.

But the seeming spontaneity of the anti-IDC candidates should not be confused with a lack of preparation—these progressives have mounted impressive challenges. All will be on the ballot, no small feat in a machine state like New York, and the challengers have gained the endorsements of incumbent Democrats like New York City Comptroller Scott Stringer and 12-term US Representative Jerrold Nadler, progressive institutions like the Working Families Party and dozens of resistance organizations, and groups like No IDC NY and True Blue NY. Their fund-raising numbers have also been strong, with Biaggi, Myrie, Jackson, Ramos, and Liu showing amounts roughly comparable to what Ocasio-Cortez pulled in for her primary House bid. Also important in this era (as a marker of both political leanings and grassroots support), most of the challengers’ money comes from small donations, while incumbents continue to rely on corporate cash.

The victory of Ocasio-Cortez energized challenger movements, and Ocasio-Cortez herself has endorsed Biaggi. Many in the New York City Council have endorsed anti-IDC challengers, as has much of the New York state’s Congressional delegation, including, most recently, Senator Kirsten Gillibrand. The New York Times endorsed three of the IDC challengers, as well as Blake Morris, a lawyer and community activist who is challenging Simcha Felder, a Brooklyn Democrat who, though not officially part of the IDC, has allied with State Senate Republicans for years.

Without the epic pro-Republican gerrymander that was signed into law by Cuomo, the State Senate should have gone blue years ago. Now, with real Democrats poised to take control, the fourth-largest state in the country will have its first durable Democratic majority in the State Senate since before World War II. They will control both halves of the legislature and the governor’s mansion, and that makes the next legislative session among the most important in the history of the state—and it maybe makes New York’s next legislative session one of the most consequential in the country. Working Families Party New York State Director Bill Lipton noted that during the last, brief period Democrats controlled the Senate in 2009, “We passed a lot of good bills; we raised taxes on the rich during the Great Recession.”

With corporate-friendly IDC senators out of the way, there’s no reason New York politics can’t be as progressive as California’s. New York could lead the country on climate-change legislation, immigrant rights, and universal health care. Of course, what really matters is what happens after the elections, but die will be cast during the primary. A vote on Thursday, September 13 could have progressive effects what will be felt for years.