In 2002, The Arizona Republic published a letter from Kyrsten Sinema, then a social worker preparing to run for a seat in the state House of Representatives, putting forth a critique of capitalism. Capitalism, she wrote, gave us NAFTA, the World Bank, and the World Trade Organization, which benefit the American ruling class at the expense of workers in the United States and abroad. “Until the average American realizes that capitalism damages her livelihood while augmenting the livelihoods of the wealthy, the Almighty Dollar will continue to rule,” she concluded. “It certainly is not ruling in our favor.”

In her first bid for office, Sinema ran as an independent candidate affiliated with the Arizona Green Party. She lost, finishing last in a five-way race. By the next year, building on her previous work for Ralph Nader’s presidential campaign, she had become a vocal anti-war activist. She organized 15 rallies by the start of the Iraq War, the biggest a February 2003 protest in downtown Phoenix attended by an estimated 2,500 people. The flyers promoting the rally, as CNN’s KFile reported, called for direct action “against Bush and his fascist, imperialist war.”

Sinema joined the Democratic Party in 2004, and shed her self-described “bomb-thrower” reputation over time. Erika Andiola, a longtime immigration activist based in Phoenix, first met Sinema through her work on immigration in the early 2000s, while the lawmaker was working in the state legislature. Andiola said Sinema was always “extremely helpful and supportive” of her work on deportation cases, noting that the Arizona Democrat did a lot of work with immigrant communities and on the border as a social worker. “She was like a champion for a lot of us who were pushing in the state legislature against some of these anti-immigrant bills,” Andiola said. During her time in the Arizona state legislature, Sinema was considered one of the most progressive members of her caucus, and fought zealously for many of the same things her Senate colleagues now support. In 2011, the Phoenix New Times named her a “local lefty icon.”

Sinema was first elected to Congress in 2012 to represent Arizona’s 9th Congressional District, which is completely housed within Maricopa County, covering Tempe and parts of Phoenix. As a newly elected US representative, Sinema hired Andiola to be her district outreach director. But Sinema’s past as a left-wing activist would come back to haunt her in the hotly contested 2018 Senate race against Republican Martha McSally. McSally sought to portray Sinema as insufficiently patriotic, resurfacing her past anti-war activism, and at one point accusing her of “treason.” But McSally was already unpopular, and her decision to focus campaign messaging on Sinema’s being too far left didn’t resonate with voters. After defeating McSally by a margin of 2.3 percentage points, Sinema became the first woman Arizona ever elected to the Senate, the first Democrat to win a Senate race in Arizona in 30 years, and the first bisexual senator elected from anywhere.

It looked, on its face, like a victory. Before Georgia Senator Jon Ossoff was sworn into office, Sinema was the chamber’s youngest Democrat at 44 years old. She stands out from her Senate colleagues, sporting vibrant purple wigs, bold patterned dresses, and thigh-high boots, in an institution known for its bland, impersonal style.

But today, Sinema is one of the most conservative Democrats in Congress, and with the Senate evenly split, she is now in a position of incredible power. Just recently, she broke with many of her Democratic colleagues by voting against including a minimum wage increase in President Joe Biden’s pandemic relief bill. Eight Democrats joined Republicans in opposing the measure, but Sinema’s defection—curtsying on the Senate floor and offering an exaggerated thumbs-down—struck a particularly sour note.

The display went viral, frustrating progressives and activists, who accused her of being all too eager to preserve poverty wages for millions. It also encapsulated the cynicism of her political transformation, and the ways liberal politicians increasingly present a left aesthetic when it’s in their own interests. In response to the outcry, Sinema spokesperson Hannah Hurley told HuffPost that it was nothing more than evidence of a sexist double standard. “Commentary about a female senator’s body language, clothing, or physical demeanor does not belong in a serious media outlet,” Hurley said.

Sinema, along with West Virginia Senator Joe Manchin, is poised to be a deciding vote on all legislation the Biden administration asks Congress to enact, giving her and her right-leaning colleagues the ability to obstruct the entire Democratic agenda. Unless Senate Democrats do away with the filibuster, a long-standing Senate rule requiring a 60-vote supermajority to advance most legislation, it’s hard to see a path forward for many Democratic priorities, including major investment in infrastructure, aggressive climate action, and expansions to voting rights. The failure to pass sweeping action could then jeopardize Democrats’ razor-thin majorities in the 2022 midterm elections, which don’t historically go in favor of the sitting president’s party—potentially giving up control for a generation.

Despite these stakes, Sinema has doubled down on her long-standing opposition to scrapping the filibuster. A spokesperson for Sinema recently told The Washington Post that she’s “against eliminating the filibuster, and she is not open to changing her mind about eliminating the filibuster.” Manchin, another obstacle in the filibuster fight, was similarly unequivocal, until he signaled some openness to reform earlier this month, saying he would consider altering the filibuster to make it more “painful” for the minority party to use. Sinema’s fellow Arizona senator, Democrat Mark Kelly, has remained vague.

Arizona progressives are ramping up pressure on Sinema and calling on the young lawmaker to support abolishing the filibuster, saying that she would be betraying the voters who helped elect her to the Senate if she goes on to sabotage Biden’s agenda. “Allowing Republicans to hold relief hostage is not what Arizonans voted for when they elected two Democratic senators,” Progress Arizona said in a statement. No Excuses PAC, a new group that recently hit Manchin with a tough radio ad in his home state, has been targeting Sinema with ad campaigns as well.

“Senator Kelly is up for reelection in 2022, so that campaign starts, like, tomorrow,” said Progress Arizona Executive Director Emily Kirkland. “And in thinking about what it’s going to be like to go back to voters to reelect him, it’s just so important that we are able to point to promises fulfilled and how he impacted your life. So I think we’re trying to understand: How does Sinema see that dynamic and is she willing to recognize that holding onto power may hinge on her decisions about the filibuster and some of these policy priorities?”

During her time in Congress, Sinema has voted with former President Donald Trump’s position about half the time, according to FiveThirtyEight’s tracker, and even joined Senate Republicans to confirm some of his nominees. In 2018, Sinema went further right than most other Democrats running in Republican-held states, campaigning on her opposition to Chuck Schumer as Democratic leader (despite being his handpicked candidate).

Brianna Westbrook, an Arizona Democratic Party official and former national surrogate for the Bernie Sanders campaign, said Sinema’s political transformation was “a complete 180” and is “hard to put in words.” There is “no doubt,” Westbrook says, that Sinema will face progressive pressure at home if she tries to hold up legislation.

There were signs of what was to come when Sinema entered national politics. During her first term in Congress, she joined the Blue Dog Coalition, a corporate-friendly group of Democrats obsessed with finding common ground with conservatives. It was also clear from the beginning, Andiola recalled, that Sinema “really believed the way to try to win or to push back on legislation was by working with Republicans.” Sinema voted to block the admission of Syrian and Iraqi refugees and has often sided with Republicans on immigration, including in support of the punitive anti-immigrant proposal known as “Kate’s Law,” which Trump pushed as part of his crackdown. In 2018, she voted with House Republicans to support Immigration and Customs Enforcement, a rogue agency that has faced countless allegations of abuse and inhumane treatment. For Andiola, Sinema’s rightward turn, particularly on immigration, has been disappointing to see. “I don’t know what she believes anymore,” Andiola said.

“At this point it’s not just the internal sort of bipartisanship, like making friends with other senators now or other members of Congress before—now she’s also reflecting that in her own narrative and that’s the part I find really hard,” Andiola continued. “Because I don’t work for her anymore so I hear the narrative and I think I know why she’s doing it, it’s just really hard to watch.”

Sinema primarily targeted moderate Republican voters and suburban women during her 2018 campaign, so her strategy was to stay as far away from progressivism as possible. But young Latino voters, many of whom skew left, turned out in record numbers and played a decisive role in her victory. It was a decades-old grassroots movement that emerged in response to former Maricopa sheriff Joe Arpaio’s crusade against immigrants, as well as long-standing demographic changes, that flipped the state blue in the 2020 election for the first time in almost a quarter-century. As the state shifts left, Sinema, who will be up for reelection in 2024, could be cornered into another political evolution.

“Our state party supports Medicare for All and the Green New Deal unapologetically. It’s in our platform,” said Westbrook. “We are a very progressive party, and the fact that she’s not representing the Democratic Party in a lot of these votes is tragic.”

Last month, both Arizona senators joined Republicans and a handful of Democrats in voting for an amendment to block stimulus checks for undocumented workers. Though the measure wasn’t included in the final version of the relief package, progressives and immigrant rights advocates took it as a sign that all their work was already being taken for granted.

“I encourage her and even Senator Mark Kelly to understand that Arizona is changing,” Andiola said. “We’re not the state that elected John McCain and Jeff Flake. There’s a lot of young people of color who are now able to vote, and there’s a lot of organizing happening that’s going to change the future of the state.”

Sinema’s office did not respond to an interview request or request for comment.