When Republican Rep. Trent Franks resigned amid reports that he had offered a female staffer $5 million to be his baby surrogate, no one thought his deeply red Arizona district could be swept in the blue wave.

Yet, last week, an internal poll from Lake Research Partners, a left-leaning organization, found Republican Debbie Lesko and Democrat Hiral Tipirneni neck-in-neck. That poll might be an outlier, but the race in this deep-red district appears to be tightening. On Monday, the eve of election day, an Emerson poll found Lesko only up by six points.

On Tuesday April 24, Lesko and Tipirneni will face off for Frank’s House seat. Among voters who have already voted, and those who plan to vote, the Lake Research survey conducted in mid-April found Tipirneni ties with Lesko 44 to 44 percent.

To be sure, it’s important to take this poll with a grain of salt. By every measure, Arizona’s Eighth Congressional District is considered to be safe Republican territory. It encompasses the suburbs north and west of Phoenix in Maricopa County — the stomping grounds of infamous former Sheriff Joe Arpaio and home to the reliably conservative Sun City retirement community. Trump won the district by 21 points.

The question most election observers are zeroing in on isn’t necessarily if Lesko is going to lose but whether Democrats can narrow the margin by which Trump and Franks won. Her once comfortable double-digit lead in the few polls has shrunk despite having some structural advantages. And that alone is worrying the GOP.

When Democrat, Conor Lamb, won a Trump +20 district in Pennsylvania only last month, the Republican party began to panic.

The National Republican Congressional Committee launched a $170,000 TV ad buy for Lesko’s campaign, Politico recently reported. The Congressional Leadership Fund has also spent $100,000 on a digital campaign to turn out conservative voters. The Republican National Committee has invested more than $300,000 in Lesko’s run and House Speaker Paul Ryan headlined an April 18 fundraising event for Lesko, which went $2,500 a seat. House Majority Leader Kevin McCarthy also headed to the district to campaign for the Republican. The Cook Political Report has moved the district from Solid Republican to Likely Republican. Outside groups have spent more than $700,000 supporting Lesko, compared to Democratic groups that have spent just over $14,000 on Tipirneni.

“The question isn’t if the GOP will retain the seat, but how much does Lesko win by?” Mike Noble, a Republican pollster in the state, told the Guardian. If the race is as close as recent polls suggest, this could raise major red flags for the Republican party in November.

Republicans have a big advantage in this district

Arizona’s Eighth District is as red as they come.

It’s Trump country; he carried the district by 20 points in 2016. And while Democrats recently saw success in a Trump +20 district, clinching the special election in Pennsylvania’s 18th last month, it’s difficult to see how they could replicate that success in Arizona’s Eighth. It’s also a district that has “no Democratic heritage,” as Dave Wasserman of the Cook Political Report told Vox — like labor unions.

Republicans have strong roots in the region and make up 41 percent of registered voters — a clear advantage over Democrats, who only make up 24 percent of registered voters. It’s home to Maricopa County and Arpaio, who as sheriff was known for infringing on the constitutional rights of residents by assuming immigration status.

Despite Arizona’s fast-growing Latino population statewide, this district is nearly 90 percent white. Almost half the population is 55 or older. It includes the Sun City retirement community, a massive chunk of the district that consistently votes Republican.

Another way this election spells trouble for Democrats is that about three-quarters of the voters will submit their ballots by mail. The county the district is in has a permanent early voting list, which many in Sun City residents are on. In other words, there isn’t as much potential for a drop-off of Republican voters.

Franks, who represented the vast majority of these constituents in the House of Representatives since 2003, was a clear reflection of these deeply red roots. He was considered to be one of the “most conservative” members of the House of Representatives — a House Freedom Caucus member, ardent Trump defender, and staunchly anti-abortion (he once tried to pass a 20-week abortion ban in the District of Columbia, even though he does not represent it). It was these positions on reproductive rights and “pro-life” surrogacy that eventually led to his resignation, after reports that he had asked female staffers to carry a child for him and his wife, possibly through natural conception.

Put together, this race is much less about the possibility of an upset Democratic win than a test of the strength of a Republican base in a scandal-plagued year.

Debbie Lesko, the Republican candidate, explained

The GOP dodged one bullet when Lesko won the Republican primary.

Lesko’s main primary challenger was state Sen. Steve Montenegro, who himself was embroiled in an inappropriate relationship with an entry-level staffer, conduct that made having him as the nominee seem like too big a risk.

On its face, Lesko’s political profile seems like an easy fit for a Trump district. A former state House and Senate lawmaker, whose district overlaps with Arizona’s Eighth, Lesko is anti-abortion and has run on a “tough on immigration” platform, saying she will work with Trump to bring the border wall to Arizona. She supports Trump but says she doesn’t approve of all his antics, celebrated the Republican tax cuts, and is quick to paint her Democratic opponent, Tipirneni as a “Bernie Sanders, Medicare-for-all” liberal (Tipirneni supports a public option). Lesko has already won the support of the conservative House Freedom Caucus.

Among notable moments in her career, she was among the 36 Republican lawmakers in Arizona who signed on to the unsuccessful lawsuit against then-Gov. Jan Brewer (R) for supporting Medicaid expansion under the Affordable Care Act. And in the district, she’s known for something much more close to home for an aging retirement population: She pushed for state legislation to make it legal for people to drive golf carts alongside the road.

But Lesko is currently facing campaign finance violation complaints, which surfaced during the Republican primary, having transferred $50,000 from her state Senate campaign to a Super PAC supporting her. She has denied any wrongdoing.

“All I can say is we did everything legally,” she said. “I have one of the best, if not the best, election lawyer firms on my campaign team. And I’m very thankful the voters didn’t fall for the last-minute false allegations against me.”

The alleged campaign finance violations haven’t had much impact in the polls. Nevertheless, the national Republican Party has seemingly sensed some vulnerability. Pro-Lesko groups have funneled more than $700,000 into the race.

Democrat Dr. Hiral Tipirneni is making this race about health care

A former emergency room doctor and cancer research advocate, Tipirneni is zeroing in on what Democrats think will be a winning message in 2018: health care.

Trent Franks “has walked away from us on his responsibility on health care and in so many other ways,” Tipirneni said in her campaign ad, saying she has experienced both sides of the health care system as a physician and through her mother’s cancer diagnosis.

Her campaign has focused on deriding Republicans’ efforts to repeal the Affordable Care Act and cut Medicaid, and their voiced interest in slashing Medicare and Social Security. She supports Medicare expansion and instituting a public option, which would run alongside the private sector.

“I’m a physician; I understand health care policy very well,” Tipirneni said in a debate against Lesko. “Basically, my plan focuses on expanding Medicare so it turns into that public option. We enhance competition. We encourage free market competition.”

For a candidate in a conservative district, she’s notably pro-abortion rights and anti-border wall. She supports a pathway to citizenship for DREAMers who “qualify and have earned it,” and says “money for ‘the wall’ would be better spent on other border security measures,” according to her campaign website. She’s an Indian immigrant (her family came to the United States when she was 3 years old), and Democrats hail her as having lived the “American dream.” She’s already won the support of Emily’s List and the Giffords gun safety group.

The national Republican Party has tried to paint Tipirneni as out of touch with the “values” of the district. More conservative groups have said she would be a vote toward impeaching Trump.

“If Tipirneni wins, she will be a vote for Nancy Pelosi and a vote to impeach the president if the Democrats take over the House,” the House Freedom Fund wrote on its website, calling for donations for Lesko.

Tipirneni’s health care-focused campaign may not be enough to overcome the district’s deeply red roots, but it could weaken Republicans’ stronghold on the district, which would be yet another sign of Democratic enthusiasm across the nation.