Scottsdale, Arizona(CNN) When Kyrsten Sinema won her US Senate seat in 2018, she was the first Democrat from Arizona elected to the chamber in three decades. It was a triumphant gain for her party -- bolstered further when Democrats took over the White House and the Senate two years later, giving them a trifecta of power.
But now many Democratic voters in her state feel Sinema is squandering the moment, holding back major agenda items crafted by President Joe Biden and supported by progressives.
"This is our moment to deliver on all of the promises that we made," said Emily Kirkland, the executive director of Progress Arizona. "She is just absolutely standing in the way of that, without making clear what she wants."
Kirkland, who often spent 13-hour days campaigning for Sinema three years ago, now feels "incredibly frustrated" with the senator's hesitation to go along with her party on a major $3.5 trillion spending bill that Democrats hope to pass to enact a wide range of key liberal priorities.
Sinema and West Virginia Sen. Joe Manchin, another centrist Democrat, have been two powerful figures at the center of negotiations -- and they have both signaled they won't support a price tag of $3.5 trillion, angering progressive members of their party in the process.
The events in Washington this week mark the latest episode in a string of decisions that have disappointed Sinema's base. In March, she voted against a bill that would have raised the minimum wage to $15 per hour, saying she didn't want it packaged with a Covid-19 relief bill.
She's bucking many in her party by refusing to support an end to the Senate's 60-vote threshold for most legislation, also known as the filibuster. Without the filibuster, Democrats could pass their priorities with only a majority, but it would mark a significant procedural change that could come back to hurt Democrats in the future should they lose the majority.
"It lends itself to dysfunction," Kirkland said, referring to the filibuster. "We should have a system where you send a party to DC, and they are able to enact an agenda."
Part of the public confusion over Sinema's platform stems from her past as a Green Party activist in the early 2000s and a liberal state legislator who fought for LGBT rights and fought against controversial immigration-related laws in Arizona.
Over time, she adopted a more bipartisan outlook and carried it with her when she was elected to the US House of Representatives in 2012. In Washington, she joined centrist groups, like the Blue Dog Coalition and built relationships across the aisle.
So when she ran for the Senate in 2018, many progressives told CNN they did not expect Sinema to vote with Democrats 100% of the time, but they at least felt confident she would come around on major issues, especially once Biden won her state in 2020.
Brianna Westbrook, a progressive voter and a precinct captain in Arizona, reflected on Sinema's career while standing outside on the patio of The Main Ingredient in Phoenix, a restaurant close to Sinema's former congressional district.
"She'd never been in the majority. She is now," said Westbrook, who also campaigned for Sinema in 2018. "And she has shown that she cannot lead when her party is the majority."
Westbrook said she and other voters who supported Sinema now feel betrayed. "She's used everybody as a ladder to climb to a position of power."
It's not just progressives who feel dissatisfied with Sinema's performance. On the other side of the patio at The Main Ingredient was Fran Williams, a voter who was sitting with her beer, a dog named Luke and some friends. Williams described herself as a moderate Democrat who also voted for the late Republican Sen. John McCain.
She supported Sinema in 2018 but now feels turned off by what she described as Sinema's "flip-flopping." And she argued the senator's sometimes-eccentric outfits -- Sinema is known for wearing colorful wigs and embracing a unique fashion style -- along with her unorthodox public persona reflect a lack of decorum that she feels McCain championed.
More than anything, Williams feels that Sinema has not communicated clearly enough with her constituents.
"She's going to have to make some kind of tremendous turnaround to get our support back," Williams said. "People are not happy with her."
When reached for comment about her constituents' views, John LaBombard, a spokesman for Sinema, said in a statement that "Kyrsten has always promised Arizonans she would be an independent voice for the state — not for either political party."
"She's delivered on that promise and has always been honest about where she stands," he added.
The frustration from voters in the state across the Democratic spectrum is palpable, but it's also reflective of the complex political dynamics that now define an ever-changing Arizona: Progressives feel she's not liberal enough, moderates feel she is not moderate enough, and many Republicans now find themselves embracing a Democrat.
That includes Kristina Murray of Buckeye, Arizona, who came to watch her 15-year-old son play baseball at a field in Scottsdale. Murray, who's not particularly wild about either party, voted for former President Donald Trump and considers herself a Republican. She said she's been surprisingly pleased with how Sinema has been willing to stand up to her own party.
"We want somebody who's independent thinking, right? We don't want somebody to be in lockstep with their party," she said. "Because then you're presenting a very ideological position, rather than a measured, intelligent, and analytical approach."
CNN spoke with several Republicans who appreciated Sinema's style but admitted it would not be enough to support her in 2024 over a Republican. It's a point that progressives continue to bring up -- Sinema is courting voters across the aisle who will never vote for her, no matter what she does.
Murray, however, disagreed and said she would "absolutely" be open to voting for her reelection.
"I'm not so ideologically rigid," she said. "You know if you present good ideas, I don't care what party you're from."