A Gen-Z social media influencer’s hopes of assuming a seat in Congress were dashed on Tuesday as she fell short in her bid to win a high-profile Democratic primary in Arizona’s Seventh District. 

The race, which was called to fill the seat of Representative Raúl Grijalva, who died of lung cancer in March, shaped up to be a contest of establishment politics versus generational change. 

A verdict was reached on Tuesday night as voters in southern Arizona pitched their support behind the frontrunner candidate, Adelita Grijalva, a former Pima County supervisor and the daughter of the late congressman. 

The 54-year-old progressive built her campaign on continuing the work of her father, a liberal stalwart who served in the House for nearly two decades. She also secured the backing of liberal bigwigs like Senator Sanders and Representative Alexandria Ocasio-Cortez. 

Ms. Grijalva is heavily favored to win against the Republican nominee, given her district’s history of voting for Democrats. If elected, she would be the first Latina to represent Arizona in Congress. 

Ms. Grijalva’s landslide win dealt a blow to 25-year-old challenger Deja Foxx, who was considered a serious threat to the well-backed favorite. According to early tabulations, Ms. Grijalva is on track to beat out the five other candidates with 62 percent of the vote — nearly three times the 21 percent of Ms. Foxx, the runner-up. 

The social media personality slash political activist shot into the spotlight in 2017, when she stood up at a town hall debate and probed a then Arizona senator, Jeff Flake, about his support for defunding Planned Parenthood. Her popularity online took off and in 2020 she worked social media for Vice President Harris’s failed presidential campaign. 

Ms. Foxx rooted her campaign in her struggles as the child of a single mother who relied on Medicaid and food stamps, and pitched herself as a prime candidate to breathe new life into Arizona’s political scene. She contrasted her youth with the Grijalva family’s political dynasty and jumped on unease over transferring power inter-generationally.

In an editorial for Newsweek, Ms. Foxx discussed her campaign’s origins, writing, “I launched this campaign alone in my room, filling out the paperwork on my laptop, and doing it wrong. But I had one advantage: I could read the room. I knew people were tired of politics as usual, tired of legacy names and corporate PACs calling the shots. Because I am too.”

Ms. Foxx’s effort was buoyed by her six-figure followings on TikTok and Instagram and the support of a fellow Gen-Z political activist, David Hogg, the former vice chairman of the Democratic National Committee. Mr. Hogg stepped down from his role amid backlash from establishment Democrats over his political group, Leaders We Deserve, which promised to spend $20 million by 2026 on primarying “asleep-at-the-wheel” incumbents. 

Mr. Hogg compared Ms. Foxx’s late surge in support to the shocking success of a 33-year-old democratic socialist, Zohran Mamdani, who last month overtook Governor Cuomo, the frontrunner candidate, to win the Democratic nomination for New York City mayor. 

Mr. Mandani’s surprise win roiled establishment Democrats and raised questions about the party’s future. Ms. Foxx, though, was unable to replicate such an upset. Still, she took her defeat in stride, promising that “we’re not going anywhere” and “this is just the beginning,” before offering her “full support” to Ms. Grijalva. 

The Arizona primary marks the second time this year that an establishment candidate won the Democratic primary nomination in a race that was called to replace a representative who died in office. Last month, the Fairfax County supervisor, James Walkinshaw, cinched the Democratic nomination to supersede a late congressman, Gerry Connolly, successfully leveraging his experience as Connolly’s chief-of-staff and endorsements from key Democrats in Congress.

Correction: David Hogg is the name of the individual who backed Deja Foxx; the name was incorrect in an earlier version of the headline.