PHOENIX (AP) — Inside a squat building ringed with a chainlink fence and concrete barriers in downtown Phoenix, election workers on Nov. 5 will begin a grindingly slow tally of every ballot cast in the vast expanse of stucco and saguaro that is Maricopa County, Arizona.

In what has become the nation’s ultimate swing county, the count here could determine whether Democrat Kamala Harris or Republican Donald Trump will be the next U.S. president. It also is likely to determine the winner of a closely watched race that could decide which party controls the U.S. Senate.

It is one of the most consequential battlegrounds in the country. That means voters, campaigns and people around the world sometimes must wait more than a week to learn who won the county, and with it, statewide races in the swing state of Arizona. This year, election officials warn it could take as long as 13 days to tabulate all of the ballots in Maricopa.

The drawn-out count has made the county a center of election conspiracy theories spawned by Trump. It’s also made Maricopa a key part of the former president’s campaign to install those who supported overturning the last election in 2020 into positions overseeing future ones.

But the reason it takes so long is simple. With its 4.5 million residents, Maricopa has a higher population than nearly half of the states in the country and is home to 60% of Arizona’s voters. Election workers must follow voting laws — which were approved by Republican-controlled legislatures — that slow the count. And it is one of the few counties in the U.S. that is so evenly divided politically that races are often close.

That’s made the county “the center of everything,” says Joe Garcia, a leader of the Latino activist group Chicanos Por La Causa, noting it is the population center of Arizona, its center of growth and home to the state capital.

“So the power structure, the money and the growth is all here in Maricopa County,” he said. “If you can win Maricopa County, you’re probably going to win the whole state of Arizona.”

Maricopa’s position isn’t just at the center of Arizona politics. The county has been a regular stop for presidential candidates as they look to clinch Arizona’s 11 electoral votes — including Trump and Harris and their campaigns this year — and it is a fulcrum on which nail-biter races that can determine control of the House of Representatives and U.S. Senate pivot.

The fast-growing county also has become home to a stew of key demographic groups in the battle for the White House: a growing Latino population, retirees, younger, newly arrived voters and a broad and deep conservative population wrestling with a pivotal splinter group — college-educated, more affluent Republicans who’ve soured on the party’s more pugnacious, and at times anti-democratic, turn under Trump.

It wasn’t always like that.

Judy Schwiebert grew up in western Phoenix in the 1960s, when the now-booming city was what she describes as “a pretty small town” and the biggest event of the year was the three-day rodeo.

Everything stopped for the rodeo parade, as horse-drawn carriages, marching bands and dancers made their way through town. Schools closed for the full three days, recalls Schwiebert, who is now a Democratic state representative. In 1969, the county was still home to fewer than 1 million people, less than one-quarter the size it is today. With about 4.5 million residents, Maricopa County now has a population similar to the entire state of Kentucky.

“Over the years here I’ve seen it grow and grow,” Schweibert said.

The area became a magnet for conservatives like John Kavanagh, a retired New York Port Authority Police officer. After 20 years of policing, Kavanagh and his wife headed west, to Maricopa County. They went in 1993, because his wife couldn’t stand the cold in New York and Florida had too much humidity and was “overstocked with New Yorkers.”

Kavanagh was like a lot of other people who moved to Arizona in the 1990s — middle-class folks fleeing colder places and what they saw as economic and political dysfunction for a sunny, affordable, and what they perceived as a cleaner city.

“A lot of people came from those other cities, and they don’t want a repeat of what they left,” Kavanagh said.

In 1993, the county’s population was 2.3 million. Republicans dominated the state legislature and Maricopa County politics. As a young state of transplants, it was easier than in other places for new arrivals to enter Arizona politics. Kavanagh was elected to the state’s House of Representatives in 2006. Now he is serving his first term in the state Senate; the county’s population has nearly doubled since his arrival, and its politics have changed.

Arizona now has a Democratic governor, elected in 2022. Both its U.S. senators — Mark Kelly and Kyrsten Sinema — were elected as Democrats, though Sinema has since become an independent.

Kavanagh attributes the county’s leftward shift to a wide array of factors — from societal changes he sees as driven by the media and academia to people moving to Arizona for higher-paying jobs that require more education.

“Hopefully there’s a point where people look and see what the result will be if that trend continues,” Kavanagh said, predicting a strong November for his Republican Party. “Just look to L.A., look to New York, you know, look to Seattle. That’s where the continuing shift left will still occur. So let’s do a hard stop and maybe go a few steps back to the right.”

Clearly, many who made the move to Maricopa over the past few decades were not like Kavanagh. The county’s conservative, low-tax approach attracted businesses as well as individuals, and those companies then attracted workers who sometimes were different from the older transplants to Arizona.

Kevin Henderson moved to Maricopa in 2010 at age 23, after living in Chicago and Portland, Oregon. A Democrat who works in catering, he was pleasantly surprised by life in a then-red state and its residents’ live-and-let-live attitude.

“The people were very friendly,” said Henderson, now 37. “We are fortunate that, with such an eclectic group of people, we are very understanding and accepting of other people's views.”

At the same time that people like Henderson came from other places inside the United States, increased migration to Arizona from Mexico also prompted political change.

In the 1990s, President Bill Clinton’s administration strengthened California’s border, pushing illegal migration to Arizona, which already had a robust Hispanic population. Immigration quickly became a political flashpoint, leading many in the growing Latino population living in Maricopa legally to feel that Republicans were demonizing them.

The biggest shift came in 2010, when Arizona’s Republican-controlled legislature passed a law allowing local police to stop people they suspected of being in the country illegally. The U.S. Supreme Court overturned the law, but it energized the state’s Latinos to organize against Republicans.

The law, which opponents dubbed “Show Me Your Papers,” was the harshest anti-immigrant law in the nation, and it changed Arizona politics, Latino activist Garcia said. It led to boycotts and protests. Nationally and internationally, people knew about Republican Sheriff Joe Arpaio — who pushed for the law — and his crime sweeps aimed at immigrants.

”That galvanized the Latino community like nothing ever had ever done before. It galvanized the Latino community more than all the voter groups put together,” Garcia said. “It was a curse, but it was a silver lining. It was a blessing because Latinos figured out that, you know what? If we’re not involved politically, then we lose.”

Republicans swept the state in 2010 and their hammerlock on Maricopa County seemed likely to continue even amid growing Latino dissatisfaction.

But that would change, as a new GOP leader emerged.

The first rumblings that Maricopa County could swing against the long-dominant Republican Party came in 2016.

Even as Trump was winning the county and Arizona, Republican Sheriff Arpaio lost his bid for a seventh term. Arpaio was something of a precursor to Trump, known for his hunger for media attention and jousting with journalists, a hardline stance on immigration and a willingness to go after his critics — he even arrested a Republican county supervisor who criticized him. Trump ultimately pardoned Arpaio after the sheriff was convicted of contempt of court for refusing to obey an injunction against racial profiling of Latinos.

Gordon Keig voted against Arpaio. A lifelong Republican, Keig was increasingly uneasy with his party’s growing hostility to immigration and SB 1070, the controversial 2010 law. Though he’s a developer and fan of low taxes, Keig was frustrated at how the GOP state legislature kept cutting Arizona’s already-low taxes, jeopardizing education funding.

Keig couldn’t bring himself to vote for Trump or his 2016 rival, Hillary Clinton. And once Trump came into office and began what Keig saw as his erratic, feud-driven approach to governing — including fighting with Arizona’s popular senior Republican Sen. John McCain, whose grandchildren Keig’s own daughters knew — Keig couldn’t take it anymore. He switched his registration to the Democratic Party.

He did get some pushback. Keig said some friends questioned how he could become a Democrat, but others understood.

“I just felt like the Republican values weren’t, weren’t there for me anymore,” he said. “But I think, you know, even some of my close friends that are still very, you know, active Republican Party members, understand and accept because they, I think they may agree with me that (what) buoyed a lot of the party has gone in a completely different direction.”

In 2020, Keig voted for Democrat Joe Biden. The change by voters like him is visible by comparing Maricopa’s votes in the 2012 presidential election with 2020. A crescent of more affluent neighborhoods ringing central Phoenix from the north to the southeastern edge, where a new Intel chip plant has attracted high-tech workers, switched from Republican to Democratic. Local political operatives dubbed the area “the flip zone.”

The flip zone largely tracks where Maricopa’s more educated residents have clustered. Once less educated than the national average, the county now boasts a slightly higher share of adults with four-year-college degrees than the national average — a key indicator of voting Democratic in the age of Trump.

As Maricopa County’s political leaning changed, so did the state’s. In every presidential election since 2000, the Republican had won both the county and the state, though Trump’s 2016 margin over Hillary Clinton was smaller than previous GOP victories. But in 2020, Democrat Biden won the county, and Arizona.

Trump falsely claimed he won Arizona after his 2020 loss, and he and his allies assailed anyone who argued otherwise.

Watching the reaction of some local Republicans after Biden won the state made Keig even more comfortable with his change.

When the Republican speaker of the Arizona House refused to award the state’s electors to Trump, the former president’s backers primaried him and forced him out of office. When Maricopa County’s Republican supervisors refused Trump’s demands to question the vote tally, they, too, were targeted. Threats against Maricopa County Supervisor Bill Gates got so bad he fled his house.

“These are people I really, really admired,” Keig said. “And they were just run through the mud.”

Trump’s lie that he won Arizona made Maricopa County one of the nation’s hotbeds of election denial and conspiracy theories.

After the 2020 election, Trump supporters turned up outside the county elections office, some armed and many waving Trump and American flags, for a “Stop the Steal” rally. His then-attorney, Rudy Giuliani, held hearings at a Phoenix hotel.

The Republican-controlled state Senate launched an error-riddled review of Maricopa’s handling of the 2020 election that included inspecting ballots for signs of fibers showing they were secretly made in China. The county became something of a tourist attraction for election deniers who came from other states to watch the show.

County Recorder Stephen Richer, a Republican who defended the accuracy of the county’s election results, was singled out for criticism by Trump himself, and Richer and his family faced threats.

In 2022, Republicans who sided with Trump against Richer and the county supervisors ran for top statewide offices, and all lost. The losing candidate for governor, Kari Lake, made so many claims about the election being stolen and allegations against Richer that he sued his fellow Republican for libel.

Lake is running for Senate this year against Democratic Rep. Ruben Gallego.

Richer says the reason some Republicans remain skeptical of the way elections work in the county isn’t because there’s anything especially complicated or unusual in how it counts votes. It’s because Maricopa — located in a onetime reliably red state where Biden in 2020 defeated Trump by a margin of about 11,000 votes — may be the best place to undermine confidence in national elections.

“I don’t think it’s the complexity of the process. Our process looks pretty similar to most Western states,” Richer said. “I think it is that this is where the action is.”

Indeed, Trump, in a campaign appearance in the county in 2023 called the county’s Board of Supervisors, which shares election duties with the Recorder, the most important in the country.

The four Republicans on the board also rebuffed Trump’s pleas to overturn the election in 2020. Two are retiring after threats, and a Trump ally won the GOP primary to replace one of them. A third was ousted in a primary by another Trump supporter.

In July, Richer lost his Republican primary. The winner, state Rep. Justin Heap, has questioned the ballot-counting process.

Part of what fuels the conspiracy theories is sheer disbelief that Maricopa, a national magnet for conservatives for decades, could go Democratic.

Michelle Ugenti-Rita is an Arizona native who sought a seat on the county Board of Supervisors but lost in a GOP primary in July. Speaking to a group of Republicans gathered in Scottsdale to watch the debate between Trump and Biden earlier this year, she denied the shift is due to actual votes.

“I am tired of the media colluding with the Board of Supervisors and gaslighting us to make us feel like we’re liberal, like we’re California,” Ugenti-Rita told the crowd.

Still, many in Maricopa are keenly aware they’re living on a partisan razor’s edge, closely balanced between the two sides. Take Sandra Heyn, an 80-year-old retired teacher from California who came to the county three years ago to be closer to one of her grown sons.

She’s a Republican and devout Lutheran who’s uneasy about Trump, even though she voted for him in 2020. But she’s bemused at how, when she meets people just in line at the supermarket, the conversation quickly turns to politics.

“I’ve had people, some people tell me, ‘Oh, you’re from California. We don’t want anybody liberal coming here.’ And then I’ve had other people say ... ‘If you’re not liberal, keep moving.’”

The conspiracists have seized on how Maricopa reports its ballot counts in one large burst after Election Day and then in dribs and drabs for more than another week, when it finally becomes clear who won. There are three main reasons for this — Maricopa’s size, the closeness of races in the county and Arizona’s voting laws, which were written and approved by Republicans.

Maricopa is the second-largest election jurisdiction in the nation. Only reliably Democratic Los Angeles County is larger.

Maricopa reports its results far faster than Los Angeles, but it takes longer to find out who won Maricopa, which creates a false impression of disorder in the vote count there.

The reason Maricopa takes longer is because Maricopa — and Arizona overall — is so evenly divided nowadays that a few thousand votes make the difference. So news organizations have to wait until virtually the last ballot is counted before declaring a winner.

In 2022, a Democrat won the state attorney general’s race by 280 votes. In less competitive places, from Florida to California, the victor is usually clear within minutes of polls closing because the tens of thousands of outstanding ballots wouldn’t be enough to close the gap.

This election, voters are casting an extra-long two-page ballot that takes longer to tabulate, so it could take up to 13 days before they finish counting, Deputy Elections Director Jennifer Liewer said. The timeline is similar to the number of days it has taken in recent elections to complete the count. Associated Press research found it took 13 days for Maricopa County to finish counting in the 2018 general election, 11 days in 2020 and 13 days in the 2022 midterms.

Arizona’s mail voting law also drags out the count. It allows voters to return mail ballots by the close of polls on Election Day. In 2022, some 293,000 voters — representing one-fifth the total vote in Maricopa — dropped off their mail ballots on Election Day.

Mail ballots take longer to count because, before they can be tallied, the envelopes must be scanned, the ballots sorted and the voters’ signatures inspected to ensure they’re legitimate. Some states like Florida require all mail ballots to be in before Election Day so this process is over when the polls close. Because of Arizona law, when Maricopa’s polls close it’s just beginning.

Extending the count even longer is a provision in Arizona law that allows voters to “cure” their ballots up to five days after Election Day. That means if the election office thinks the signature on the ballot or some other technical detail is wrong, the voter has five more days to come in and fix it so the ballot counts.

Usually the number of cured ballots is relatively small, but in elections where every vote is essential to determining the winner, the curing process drags the suspense out even more.

Richer noted that, while these processes may sound overly complex to some in the U.S., they’re things that Western states like Arizona have been doing for a century or more. Mail voting dates back to the 19th century in the region.

“We vote differently than most of the Eastern United States does,” Richer said.

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Associated Press reporter Maya Sweedler in Washington contributed to this report.