On Friday evening, Karen Giorno, a former senior adviser on Donald Trump’s presidential campaign, addressed a few dozen volunteers for Bob Gray, one of 18 candidates running for Congress in a special election this week in Georgia’s 6th District. The seat, which once belonged to Newt Gingrich, was supposed to be safely Republican. Former Rep. Tom Price, who stepped aside to become Trump’s secretary of health and human services, won November’s election by 23 points. Now, however, a Democrat, Jon Ossoff, is leading in all the polls. And there’s at least a chance that he could clear 50 percent of the vote come Tuesday, which would mean that Ossoff would not have to face a runoff and would be going to Congress as the first Democrat to hold Georgia’s 6th since 1979.

Gray—a businessman who’s trying to position himself as the most loyal Trump supporter in the race—is fighting it out with three other Republican candidates in the hope of finishing a distant second to Ossoff and keeping the Democrat below 50 percent to force the runoff. Giorno had flown in to rally the troops. “This is a really important election,” she said. “It’s becoming a national spotlight, because it’s going to be a referendum on Donald Trump and his presidency.”

She’s right. If Ossoff—a 30-year-old former congressional aide and documentary producer—were to win, it would set off a political earthquake. Right now, though Trump is unpopular nationally, Republicans in Congress haven’t wanted to break with him, because they fear primary challenges more than general election defeats. If a first-time Democratic candidate could take Gingrich’s old seat, that calculation would likely change and Trump would be seriously weakened, since at least some Republicans would have an incentive to turn on him to save themselves.

Democrats have poured money into the race; Ossoff has raised a staggering $8.3 million. The DCCC is targeting black voters—about 10 percent of the district’s electorate in presidential races—with an advertisement featuring Samuel L. Jackson. “Remember what happened the last time people stayed home. We got stuck with Trump!” he says, before nodding to his Bible-quoting Pulp Fiction character: “We have to channel the great vengeance and furious anger we have for this administration into votes at the ballot box!” On the ground, volunteers—a great many of them suburban women who have never been politically active before—are knocking on so many doors that even friendly voters complain about overkill.

The Georgia Republican Party is trying to boost turnout by appealing to the base’s sadism; one mailer features a photograph of a sobbing man and the words, “MAKE A LIBERAL CRY…” Trump himself appears a little worried. On Monday morning he tweeted: “The super Liberal Democrat in the Georgia Congressioal [sic] race tomorrow wants to protect criminals, allow illegal immigration and raise taxes!” His campaign sent out an emergency fundraising appeal: “They’re hoping to pull off a major upset to President Trump and YOUR Republican party tomorrow, but we’re fighting back and need your help.”

But the reason Ossoff has a chance in the first place is that Trump is relatively unpopular in the district, where he beat Clinton by only 1.5 percent. The Georgia 6th is mostly made up of affluent Atlanta suburbs; according to Emory University political scientist Alan Abramowitz, it has the highest percentage of college graduates of any district in the state. “That’s one of the reasons that Trump really underperformed relative to the normal Republican vote in that district,” Abramowitz says. “Clearly there are quite a few college-educated independents and even some Republicans who are really turned off by Trump.” The district is far less Trump-friendly than Kansas’ 4th district, where Trump won by 27 points but where Democrats were still able to mount a surprisingly competitive special-election challenge that ultimately fell short earlier this month.

The chance of Ossoff winning outright on Tuesday is still slim. According to FiveThirtyEight’s survey average, he’s currently polling at 46 percent. That puts him far ahead of any of the Republicans: Right now the leading GOP candidate, Karen Handel, is at 18 percent, followed by Gray at 13 percent. At this point, the likely scenario seems to be that the election proceeds to a runoff on June 20, which would give Republicans the opportunity to consolidate their voters. In that case Ossoff could still win; as FiveThirtyEight’s Nate Silver argues, you can’t necessarily tell who will win a runoff just by adding up the margins of all a party’s candidates. “Even if Ossoff finishes in the low 40s, it will be hard to rule him out in the second round provided that he still finishes in first place by a comfortable margin,” writes Silver.

Yet the Ossoff campaign believes that a Tuesday victory is at least possible. “There’s a good chance that we can get to 50 percent plus one,” Ossoff’s campaign manager Keenan Pontoni told me. “We have seen a number of internal polls, and we’ve seen the complete early vote data, and that information really demonstrates that we’re creeping up closely to 50 percent. What will get us over the top is having an expanded electorate.” In other words, they’re counting on people who don’t usually vote in special elections showing up for this one.

That’s not simply wishful thinking. Despite all the attention to outside forces converging on the Georgia 6th, what’s driving Ossoff’s campaign is an intense local mobilization. The campaign has more than 4,000 active volunteers; on Saturday alone, Pontoni says, 900 people knocked on 35,000 doors. “It’s a renewed spirit of civic engagement and political activism,” Ossoff told me after a rally at his Marietta campaign office. “Most of it is being led by women. I’m taking my cues from them.”

The role of local women in making the special election competitive cannot be overstated. Again and again, Ossoff volunteers told me similar stories. Many had never been politically active before. They didn’t know what district they lived in or who their local representatives were. They kept their Democratic sympathies quiet, assuming that their neighbors wouldn’t approve. Trump’s election had shocked them out of their complacency. Stacy Efrat, a 38-year-old with three kids, said the husbands in her circle wonder where their wives went: “All the sudden they’re married to different women, who are out every night, going to meetings, protesting, and who spend all day while their kids are at school calling their congressmen.”

Before the presidential election, Jessica Ziegler, a 32-year-old mother of three, says she and her friends “felt very safe and secure not being engaged in [politics] at all, because our lives were going just fine.” They were consumed by work and family, and what extra energy they had went into the local schools. Ziegler serves in the PTA and as lead volunteer in her youngest child’s preschool class. What she calls the “catastrophic event” of Trump’s victory reshuffled those priorities.

For the first time, Ziegler and women like her feel that their families are endangered, both morally and physically, by an election’s outcome. “I cannot imagine my kids growing up in a less American country than I did,” she told me. She worries about Trump plunging America into war with North Korea and about attacks on reproductive rights that could blight her two daughters’ futures. “I absolutely don’t want my boy growing up thinking that Donald Trump is a role model, either,” she says. Since November, Ziegler has thrown herself into local politics, where she found she could make use of the organizational skills she’d learned as a school volunteer. Now she’s a precinct captain for the Ossoff campaign, driving around her neighborhood in her minivan to round up every vote. On Sunday night she sent me a text message to tell me about three last-minute rallies she’d organized for the next day; the first one started at 7:30 a.m., so that commuting drivers would see them on their way to work.

It’s not clear if the polls are measuring this passion; they might not be capturing women like Efrat who’ve never voted in a special election before and are now actively volunteering on behalf of a campaign. “A special election is notoriously difficult to poll accurately,” says Ossoff. “The polls show us within striking distance and the early voting numbers show great intensity on the Democratic side. So it’s winnable on Tuesday.” But if it’s not won on Tuesday, the campaign will retool for the runoff. Ossoff launched his campaign with a fundraising plea to “Make Trump Furious.” Whatever happens, Tuesday won’t be his last chance to do that.