Arizona used to be a conservative stronghold. Now it may go blue.

Two years ago, Yasser Sanchez was all in for Martha McSally. An influential leader in the Latino community, he took the Republican Senate candidate around to Spanish-language radio, television, and newspapers. He put up signs for her.

Now, he’s planning to vote for her opponent.

Senator McSally, Mr. Sanchez explains, is in lockstep with President Donald Trump – whom he vigorously opposes. “I thought she could be the next maverick from Arizona,” says Mr. Sanchez, about the first female fighter pilot in the United States to fly and lead a squadron in combat. But “she will do whatever the party tells her, because if not, it will make her life impossible. She holds tight to the president.”

It’s no exaggeration to say that next month’s election in this once conservative stronghold could determine control of the White House and the Senate, as well as a state legislature that’s been dominated by Republicans for more than half a century. With just weeks to go, both parties are pouring resources into a state that went for Mr. Trump by 3.5 percentage points in 2016, but has been rapidly shifting from red to purple – and now, maybe blue. 

On Thursday, former Vice President Joe Biden and running mate Sen. Kamala Harris were expected in the state, their first joint campaign appearance since the convention. Vice President Mike Pence was also scheduled to visit, for the fourth time. President Trump was supposed to hold two Arizona rallies this week, but those were put off after his COVID-19 diagnosis.

In many ways, Mr. Sanchez embodies Arizona’s changing electorate. An immigration lawyer and family man, he’s originally from Mexico – and is part of a growing Latino population that is becoming a larger share of the vote here and leans heavily Democratic. Mr. Sanchez himself quit the GOP last year, saying he’s “fed up” with the president’s values and his attacks on immigrants, among other reasons. He plans to vote for Mr. Biden for president – joining other crossover Arizonans like the late Sen. John McCain’s widow, Cindy McCain.

Perhaps most crucially, Mr. Sanchez lives in Maricopa County – a longtime Republican electoral fortress that encompasses Phoenix and its fast-growing suburbs. Maricopa, combined with reliably blue Tucson in Pima County, now accounts for more than three-quarters of Arizona votes. That urban tilt could propel Democrats to a stronger showing in Arizona than in Wisconsin, Michigan, or Pennsylvania, all of which have much larger concentrations of rural voters.

“Arizona is a rapidly changing state. Maricopa County alone is about 60% of the vote, and that’s a rapidly diversifying, well-educated area,” says Jessica Taylor, who follows the Senate for the Cook Political Report. The report now rates Arizona as “lean Democrat” for both the presidential and Senate races.

Maricopa County is the “bellwether,” says Democratic consultant Chad Campbell, at Strategies360 in Phoenix. “Once Maricopa goes Democratic consistently, if you’re a Republican, you have serious problems,” says the former legislator in the Arizona House.

Bellwether Maricopa County

Two years ago, Arizona voters sent Democrat Kyrsten Sinema to the U.S. Senate; she beat then-Representative McSally by 2.4 percentage points. It was the first time the state had elected a Democratic senator since the early 1980s. Later that year, the governor appointed Ms. McSally to the seat of the late Senator McCain, setting up this year’s election to fill out the final two years of his term.

Senator McSally’s Democratic opponent, Mark Kelly, is a former Navy fighter pilot and space shuttle commander. Many here know him as the husband of Gabby Giffords, the former congresswoman from Tucson, widely admired for her struggle to recover from an assassination attempt in 2011, when she was shot in the head at an outdoor event. Six people died in the mass shooting, and the couple have become strong advocates for “common-sense” gun regulations.

On a recent Saturday in the Ahwatukee section of Phoenix, about 25 Democratic volunteers were gathering at 8 a.m. to pick up signs and literature to drop on driveways. Democrats have not been knocking on doors due to the pandemic, but have aggressively reached out to voters through texts, calls, social media, and handwritten postcards and letters – along with a deluge of advertising.

Those who show up mirror the trends moving in Democrats’ favor.

There’s Barbara Geiswite, a recently retired dental assistant, who voted for Mr. Trump in 2016 but switched her registration from Republican to Democrat in April after her son urged her “to think for myself.” Mark Swanson, an independent, has cast votes for both parties, but this year plans to vote for Democrats up and down the ballot: “We need to restore balance in the country.” 

Helping behind the scenes is a recent graduate from Arizona State University, John Gimenez. He works in marketing for a mortgage company, and in his spare time helps the local Democratic Party with social media and digital advertising. When he was 11, his parents – immigrants from the Philippines – moved the family from Los Angeles to Arizona, where housing was much more affordable. It’s a typical story and helps explain Maricopa County’s nearly 50% population increase over the past two decades. The state is the fastest growing in the nation and is expected to gain a congressional seat after this year’s census.

When Mr. Gimenez began to come out as gay in high school, he says it was clear which political party he would support. “There was one side actively fighting against me and one side actively fighting for me.” He started the first Young Democrats club at Hamilton High School in Chandler, a Phoenix suburb that has attracted a lot of young families. The club had three members, including himself.

Republican refugees

In recent years, the influx to Arizona has included younger people from all over the country – not just retirees from the conservative Midwest. “People don’t realize it if they don’t live here,” notes Mr. Campbell, the Democratic strategist. “We have a young population, heavily Latino, that is much more progressive on a lot of issues.” 

But Republicans are also still heading to Arizona, many of them political refugees from the West and East coasts. “They are happy to come here, where they can be free to be conservatives,” says Sue Harrison, vice president of the Republican Club at PebbleCreek, a luxury retirement resort in Goodyear, a suburb of Phoenix that’s also part of Maricopa County.

Ms. Harrison is sitting on a folding chair on a busy corner near the resort, registering newcomers to vote, while a few dozen people wave Trump signs and American flags at honking cars and roaring Harleys as they pass by.

One of the flag-wavers is Denice Ballas, who moved to the resort about three months ago from Pleasanton, California. She and her husband were the only ones in their old neighborhood to put up a Trump sign – though under cover of night, she says, people would knock on their front door and thank them.

Several people in the group note with concern that more and more progressives are moving to their community. One quotes a favorite T-shirt: “Don’t California My Arizona.”

Caroline Anderegg, spokeswoman for the McSally campaign, dismisses concerns about Maricopa County turning blue, calling them “a lot of opinions by the chattering class.” Still, she emphasizes that the senator was ranked the sixth-most bipartisan senator by the Lugar Center at Georgetown University. Ms. McSally recently won the endorsement of a group of Hispanic faith leaders who applaud her stance against abortion rights and in favor of religious freedom. “Latinos are not a monolith,” says Ms. Anderegg.

Growing Latino clout

That’s true, but in 2018, three-quarters of them voted Democratic in Arizona, according to polling firm Latino Decisions and the Democratic data company Catalist. Latinos played a significant role in Senator Sinema’s victory and were a higher proportion of the electorate that year, up by three percentage points from 2014.

Despite the pandemic, grassroots organizers have managed to register more than 160,000 new Latino voters so far, about 80% of them in Maricopa County, says Eduardo Sainz, state director for Mi Familia Vota. That tops 100,000 new voters four years ago.

“We’ve made a years-long effort to hear from and reach Latino voters across the state,” said Kelly campaign spokesman Jacob Peters, in a statement to the Monitor. 

Top of mind for Latinos are health care, jobs, and education. Immigration is also part of the mix.

Immigration attorney Mr. Sanchez blasts President Trump’s 2017 pardon of former Maricopa County Sheriff Joe Arpaio, an immigration hard-liner, as a “blatant attack” on the Latino community. Latinos helped oust Mr. Arpaio, a Republican, in 2016, even as Mr. Trump won the county and the state. Mr. Arpaio, along with Arizona’s highly controversial stop-and-check-immigration-status law, known as SB 1070, turned off a generation of Latinos to Republicans, many say.

“We already went through this anti-[immigrant] wave,” says Mr. Sanchez, whose reception room features a photo album of people he has helped obtain green cards and citizenship. “We thought we moved past that – and Donald Trump came and [revived] all these things we rejected, and made them national.”

Mr. Sanchez is running get-out-the-vote events from his law-firm parking lot in Mesa, right around the corner from the temple of The Church of Jesus Christ of Latter-day Saints, whose followers founded the city in the late 1800s. He himself is a committed church member who leads services – and one of a number of Latter-day Saints who have turned against the president. In Arizona, the most prominent is former Sen. Jeff Flake. Utah’s Sen. Mitt Romney is another.

Masked-up, he distributes Biden signs, stickers, and “Adios Trump” T-shirts. Last month, he posted that same message on 10 billboards during President Trump’s visit. Next up: a caravan drive for Mr. Biden. All efforts are socially distant (Mr. Sanchez was in bed for 10 days with the virus earlier this year), but he’s concerned the lack of in-person events and canvassing is hurting outreach.

Republicans, by contrast, have been full-throttle with in-person events, including visits from the president, vice president, and various surrogates. Their turnout operation is a well-oiled machine. “People have amnesia and forget the president did win Arizona in 2016,” points out Ms. Anderegg. “While the state is incredibly independent, it is a right-leaning state.”

Republican consultant Sean Noble believes Senator McSally will ride President Trump’s coattails to victory. He estimates there are still some 100,000 new votes to be found for Mr. Trump, compared with 2016 – from conservatives who voted for the libertarian or a write-in candidate, or who left the first line of the ballot blank. Now that they’ve seen what the president has done on things like taxes, regulations, and judges – especially the Supreme Court – they may be on board.

“I just have a hard time thinking the character shot at the president is going to matter,” he adds. “It didn’t matter in ’16 even after the [“Access Hollywood”] tape came out.”

That’s certainly true for the flag-wavers of PebbleCreek. “Promises made, promises kept,” says Ms. Harrison, who describes the president as a “salty sailor who gets things done.”

Still, Democrats are hopeful that years of grassroots engagement of Latinos, combined with shifting demographics and the anti-Trump factor, will make this the year that Arizona finally turns blue.

“It’s a perfect storm,” says Democratic consultant Adam Kinsey. “We have a spectacular top-of-ticket with Biden, Harris, and Kelly, and all this engagement work being done. It’s very exciting, as a long-suffering Arizona Democrat.”