President Donald Trump on Saturday is expected to parachute into the middle of a surprisingly close congressional race in Kentucky. He wants to rally conservatives around a GOP incumbent under siege from one of the leading faces of Democratic efforts to regain control of the House of Representatives.

Democrats don’t necessarily need retired Lt. Col. Amy McGrath, a former Marine fighter pilot who rose to prominence thanks to a viral campaign ad, to win Kentucky’s 6th Congressional District. It’s possible they could pick up the 23 seats required to flip the House without her.

But on election night, McGrath’s race against Rep. Andy Barr (R) may offer the earliest indication of whether they will, and of how big that majority could be if they do.

Kentucky’s polls close at 6 p.m. EST, meaning McGrath vs. Barr will be one of the first races to end and one of the earliest swing districts to record an outright winner. A victory for McGrath could portend a big night for Democrats. Even a narrow loss in a district like this one may suggest they have enough momentum to regain the majority.

“It’s a real bellwether race, because it’s one of the targets and because it’s going to be one of the first races called,” said Scott Jennings, a Kentucky-based Republican political consultant.

“We’re gonna find out which way the wind is blowing,” he said. “If she wins, that means [Democrats] are knocking down contested jump shots.”

That it is even contested is surprising. The 6th District has been a reliable Republican seat since Barr defeated former Rep. Ben Chandler (D) in 2012, and forecasters considered it safe when the 2018 cycle began. The Democratic Congressional Campaign Committee didn’t include the district in an initial list of targets, and it recruited a candidate with the ability to self-fund his campaign in part to save money on a race it wasn’t ready to prioritize.

But McGrath upended it all when she beat Lexington Mayor Jim Gray in the Democratic primary, erasing a 40-point deficit early in the race. This happened within a broader context of surging Democratic enthusiasm, especially among women, and sinking approval numbers for a Republican-led Congress, putting more seats into play. For Democrats, the central Kentucky district ― which is largely rural but which includes blue strongholds in Lexington and Frankfort, the state capital ― was now on the map.

With less than a month to go, the race appears to be a dead heat. Internal polls from each campaign show their respective candidate ahead, while a New York Times live poll called it a statistical tie, with Barr ahead by a single point, in late September.

Both parties are prioritizing the race. On Friday, less than 24 hours before Trump’s scheduled appearance with Barr, former Vice President Joe Biden stumped for McGrath in a rural corner of the district. Democrats have prefaced Trump’s appearance by circulating audio of Barr joking that the president “has a tendency to exaggerate from time to time.” Barr, who said the 8-second clip was taken out of context, responded by saying that McGrath’s embrace of Biden amounts to support for the “failed policies” of the Obama administration, which Republicans have long blamed (with little evidence) for the demise of the coal industry.

Barr and the GOP’s attacks on McGrath have come via a relentless series of television and radio ads over the last two months. Barr and GOP political groups have already spent or committed over $3 million in television and broadcast advertising in the Lexington media market, The New York Times reported this week.

In the primary I took on the Democratic establishment and I beat them. Now I’m taking on the Republican establishment, and I’m going to beat them too. Amy McGrath

McGrath surged onto the scene in August 2017 with an ad that touted her background in the Marines and her efforts to overcome the armed forces’ ban on women in combat. The spot, which left her campaign temporarily broke, turned her into a political star, fundraising force and Resistance hero.

Her primary win made McGrath one of the most prominent of the women candidates who have pulled off upsets in Democratic contests across the country. She’s also one of a crop of Democratic candidates using their status as veterans to their advantage — her viral ad featured jarringly nonchalant b-roll of an aerial bombing — and the combination of traits has helped McGrath remain a fundraising machine in the general election. In the fiscal quarter that ended Sept. 30, she raised $3.65 million.

McGrath’s feminist bona fides have made her a darling of grassroots Democrats, but Barr has attempted to wield those same credentials against her. He has released ads that attack her for a speech where she said, “Hell yeah, I’m a feminist.” He has tied her to liberal women like House Minority Leader Nancy Pelosi (D-Calif.), talk show host (and early McGrath supporter) Chelsea Handler and former Secretary of State Hillary Clinton. His ads have blasted McGrath as a “rubber-stamp” progressive in favor of abortion rights.

Conventional wisdom says that would be enough to doom a candidate in conservative, religious central Kentucky. But it hasn’t: McGrath has countered Barr’s attack ads with the same mix of outsider politics, overt feminism and a sort of economic populism geared toward Kentucky-specific issues ― in particular, health care and rural economic development ― that she used to soar past Gray in the primary.

As a first-time candidate, she can credibly point to her own discontent with the political system that she sees as having fueled Trump’s popularity in places like Kentucky. She laughs off Barr’s attempts to sew her to Pelosi’s hip, noting that the DCCC recruited Gray into the 6th District primary to run against her.

“In the primary I took on the Democratic establishment and I beat them. Now I’m taking on the Republican establishment, and I’m going to beat them too,” she told HuffPost after a late-September appearance at a Democratic event in Georgetown, Kentucky, repeating a line that has become something of a de facto campaign slogan.

To McGrath, the discontent in her district is rooted in the belief that both parties have quit working on behalf of the common voter. National Democrats, she raged in the primary, are no longer fighting for Kentucky’s workers. Republicans like Barr, she asserts now, are serving a wealthy donor class, not ordinary folks. Her evidence: Barr’s reliable votes to repeal the Affordable Care Act, the sweeping health reform law that helped give coverage to more than 500,000 Kentuckians, and his support for the 2018 GOP tax cut package that handed 82 percent of its benefits to the wealthiest 1 percent of households, according to the nonpartisan Tax Policy Center.

“It’s a question of, who are they working for?” McGrath said. “They’re constantly working for the wealthiest and corporations. That’s who they’re passing legislation to help. The wealthiest 1 percent.”

She burnishes this with calls for expanded investment into the rural parts of the district. Rural broadband is a favorite topic; new infrastructure spending is another. On health care, McGrath doesn’t go as far as the new wave of Democrats who call for Medicare for all. Still, she has advocated for expanding Obamacare by adding a public option and reducing the eligibility age for Medicare.

There are a lot of women in this district and the rest of Kentucky who... see her as someone who will stand up for them and show that women can do this kind of job. Al Cross, veteran Kentucky political journalist

And then there is her feminism, which she’s continued to foreground even as Barr has attempted to use it against her. She’s still the “hell yeah” feminist ― the first female Marine to fly an F/A-18 in combat, a candidate willing to say she supports abortion rights and to argue for expanded contraception access, someone who believes this district is home to a lot of women who, she said, are “fed up of the picture of a bunch of old white men sitting around” making decisions that primarily affect women.

Al Cross, a veteran Kentucky political journalist and analyst, predicted that McGrath will “get a lot of votes from Republican women” on Election Day.

“There are a lot of women in this district and the rest of Kentucky who feel like their ambitions, political and otherwise, have been suppressed,” Cross said. “And they see her as someone who will stand up for them and show that women can do this kind of job.”

This approach worked in the primary. Can it work again with the more conservative general electorate? There are reasons to believe it could, not just because of the stances Barr has taken on the increasingly popular health care law and the never-popular tax cut package, but also because the landscape in Kentucky has continued to shift as the race has worn on.

The protests evoked all the major themes of McGrath’s campaign and galvanized the very kinds of voters ― women and public employees ― she’s counting on to show up in big numbers in November.

Barr has defended his votes to repeal the Affordable Care Act and cut taxes.

“Kentuckians are better off today because of the policies I voted for and this President signed into law,” he said in a statement when Trump’s visit to his district was announced. “Thanks to tax cuts, deregulation and reforms to increase Americans’ access to the financial system, we’ve delivered faster economic growth, more jobs and bigger paychecks.”

With less than a month to go, Trump is slated to hold a Saturday afternoon rally for Barr at Eastern Kentucky University in Richmond. Trump won the district by 15 points in 2016 and remains more popular than not in a district (and a state) where few other politicians can say the same. It has created a situation where the president who inspired McGrath to retire from the military and jump into the race 14 months ago may now be the GOP’s last, best hope of stopping her.

“It’s one of the most interesting races in America,” Jennings, the GOP consultant, said. “And because of how early it’s going to be called, it’s going to tell us a lot about what’s going on on election night and what’s going on in America.”