TALLAHASSEE — Democrats are carving inroads though the historically conservative city of Jacksonville, landing a handful of improbable political victories and framing a question for Election Day: Will Florida’s only Republican city fail Donald Trump?

The president must win Florida to return to the White House, but Republicans’ loosened grip on Jacksonville, the party’s only urban foothold in the battleground state, is complicating that political math. And it’s given Joe Biden a shot of confidence even as state and local Republicans vow to defend what long has been considered their political home turf.

Jacksonville is “big and growing, it has an important media market, and has sort of been the tipping point over the past number of cycles,” said Susie Wiles, the Trump campaign’s senior Florida adviser. “The campaign won’t take any part of the state for granted.”

“Jacksonville will not be neglected,” said Wiles, who also led Trump’s 2016 Florida campaign.

Jacksonville makes up almost all of Duval County and is culturally and politically different than Florida’s other reliably blue metropolitan areas. It is defined by a huge military presence, undying love for its middling football team and the “Duuvvalll” battle cry, an homage to both the county and the gritty personality its residents embrace.

But the area’s political identity is influenced of late by politically engaged Black residents, who make up nearly a third of the county’s population, and a steady flow of young professionals moving into Jacksonville as middle class conservatives migrate to the neighboring suburbans of St. Johns, Nassau and Clay counties, which favor Trump by wide margins.

“This is a pretty big deal,” said Michael Binder, a University of North Florida political scientist who regularly polls the region. “If Biden wins this county, it’s not the sort of thing where it will necessarily flip back. Once Jacksonville turns blue, it will be blue for a long time.”

“I think Biden will carry Duval County,” Binder said, “and that will play a huge role in helping him carry Florida.”

The strength of Jacksonville’s Republican resume is without question. A Democratic presidential nominee hasn’t won the city since Jimmy Carter. Before Andrew Gillum’s surprise win there in 2018, no Democratic gubernatorial nominee had won Duval County since Jacksonville attorney Steve Pajcic in 1986.

Dean Black, chair of the Duval Republican Party, acknowledges the challenge. He’s building a “juggernaut” after years of party complacency in the county allowed Democrats to advance. He has upward of 1,000 active volunteers and 11 county field offices, more than double the number the party had in 2016. Trump is scheduled to hold an event in Jacksonville on Thursday.

“We understand that Duval is a now a pivotal purple battleground county in the nation’s biggest battleground state,” Black said.

The local political infrastructure is run largely by Republicans, which helped Jacksonville land the Republican National Convention’s marquee events this year, until the GOP pulled the plug on the party amid coronavirus concerns.

Political change reared its head in 2008, during Barack Obama’s first presidential campaign. Obama didn’t win Jacksonville that year or in 2012, but he injected organizational muscle into the city.

Hillary Clinton lost Duval County in 2016, but by only 6,000 votes, a much smaller margin than Obama’s nearly 15,000-vote loss four years earlier. In the 2018 midterms, statewide Democratic candidates swept Duval, including Gillum and Sen. Bill Nelson. Both lost their races, but the wins in Jacksonville attracted attention.

“A number of people have been seeing this coming in Duval for a while. The days of countywide candidates, including at the presidential level, winning by double digits seems long gone,” said Chris Hand, a Jacksonville-based attorney who worked as the chief of staff to a Democratic mayor. “While Barack Obama did not win, he got much closer to winning than previous Democrats and helped the county kind of close the gap.”

For the 2020 election cycle, full-time Democratic organizers were on the ground in the county in September 2019, much earlier than in past presidential election cycles, Duval Democratic Party Chair Daniel Henry said. Currently, Democrats have 10 full-time organizers there, roughly double the party’s presence in the city compared to recent presidential cycles. And the team coordinates a much larger collection of county-level volunteers.

Democrats are also spending more on TV in the Jacksonville media market, so far buying and reserving $5.3 million, including $4.6 million directly from the Biden campaign. Republicans have so far purchased or reserved $4.1 million in the Jacksonville media market, of which $3.3 million is directly from the Trump campaign.

The legal battle could theoretically result in legislators losing the only raise they’ve received in the past two decades. More broadly, the results will help set the parameters for how far the Legislature can go in its increasing reliance on leaving difficult decisions up to unelected commissions.

Democrats still face challenges. Amid Covid-19 concerns, Democrats have halted traditional voter outreach activities such as door knocking, even as Republicans lean into them.

Vice President Mike Pence has held Jacksonville visits, and earlier this month the city was host to an event featuring Lara Trump, the president’s daughter-in-law, and former Florida Attorney General Pam Bondi.

“That stuff is important. It boosts recruitment and volunteer excitement,” said state Rep. Jason Fischer, a Republican whose political career began in 2012 on the Duval County School Board. “Republicans have been doing that sort of thing here, and Democrats just have not. It’s the sort of energy any political organization needs.”

The stinging losses of 2018 won’t be repeated, he said. He predicts a comfortable Trump victory.

Democrats organized well and early in 2018, but that election cycle was driven by Gillum, a progressive Black nominee who engendered excitement and turned out the city’s Black voters. In the 2014 gubernatorial race, Black voter turnout was 44 percent. In 2018, it was more than 62 percent.

Energizing Jacksonville’s Black voters will be crucial for Biden.

“[Black] turnout to a degree has depended on who the candidate is, and how much energy people feel towards them,” said Florida Senate Minority Leader Audrey Gibson, who is Black. “I think Joe Biden will capture that. There is excitement, and it’s Donald Trump on the other side.”

Increased Black voter engagement is the result of a years of organizing effort going back to 2008, said Joey McKinnon, a Jacksonville Democratic consultant and director of Faith in Public Life Florida, which focuses on political engagement in churches. Biden’s time as Obama’s vice president, and his running partner Kamala Harris, a Black senator from California, will help energize Black voters, he said.

“The church community and pastors here are trusted messengers in Duval, so things like Souls to the Polls are huge,” he said. “Biden also faithfully served the nation’s first Black president. I think that’s remembered here.”

On the Republican side, Trump’s law-and-order messaging is breaking through in a city accustomed to violent crime. Biden has run TV ads in Florida calling nonpeaceful protests “lawless,” but Republicans are casting him as an apologist for looters.

“’Law and order resonates in Duval,” said Tim Baker, a Jacksonville GOP consultant who advises local politicians. “The Democratic platform has had some contempt for law enforcement, and that really does not play with the Republican base or many independent voters.”

Baker completed a countywide poll over the weekend on several issues, including the presidential race, and found Trump and Biden in a dead heat, with Trump up 42-41. The poll had a margin of error of 4.9 percent.

The question remains: Will Trump be the first Republican nominee since 1976 to lose in Duval County?

“I reject the premise of that question,” said Wiles. “Let’s just start there.”