Allie Young believed in Kyrsten Sinema. Her vote helped elect the seemingly progressive Democrat from Arizona to the Senate in 2018. But she wonders what happened to Sinema when she got to Washington.

Young, a voting rights activist and citizen of the Diné, or Navajo Nation, is appalled by Sinema’s refusal to reform or abolish the filibuster.

“She has betrayed her constituents,” Young, 31, said by phone this week. “The sort of inaction that she’s taking right now is an action and it’s making the BIPOC community, especially in Arizona, distrust her more and more as the days go by.”

Republicans have deployed the filibuster to block legislation brought by Democrats to safeguard voting rights four times this year. On Wednesday they thwarted debate on the John Lewis Voting Rights Advancement Act, named after the civil rights hero and congressman.

It is an issue that hits home for Young, who last year organized a second “Ride to the Polls” campaign in Arizona that led Indigenous people more than 20 miles on horseback to polling places so they could cast their votes.

“Her campaign was something that attracted us because back then she seemed to be a little more progressive than she is now. That’s the part that we’re all having trouble understanding. What happened?”

The bewilderment deepened late last year when Sinema nominated Young for the Congressional Medal of Honor Society’s Citizen Honors Award for her contribution to increasing voter registration and turnout. Young reflected: “The fact that nomination came from her and her office tells me that she knows the importance of the Native vote.”

“[But] she’s not protecting our right to vote and, if she doesn’t end the filibuster and these voting rights acts don’t get passed, that will affect us. We’re already seeing some of these voter suppression laws that have been passed earlier this year and how they will affect the Native vote.”

This has led to the oft-asked question: what does Sinema really want? “A lot of folks are talking about how she’s trying to stay bipartisan. She thinks that’s the key to everything that’s happening in the divisiveness that we’ve seen,” Young says.

“It’s very devastating to all of us Arizonans and those who trusted in her. That’s the point of this election process. We vote in and we elect leaders that should be held accountable and that’s what we’re doing now. We put faith in a leader that’s going to show up for us and protect us and fight for us and we’re not seeing that right now.”

Earlier this year the US supreme court upheld Arizona laws that ban the collection of absentee ballots by anyone other than a relative or caregiver, and reject any ballots cast in the wrong precinct.

Republicans, who control the governorship and both chambers of the state legislature in Arizona, are also pushing to end same-day voter registration, a move that would hurt the Navajo Nation, with 170,000 people and 110 communities spread over 27,000 square miles, mostly in Arizona.

Young explained: “Sometimes it’s incredibly difficult to get to the poll. It’s difficult to get anywhere, to even get to a hospital or a clinic or a grocery store, so making multiple trips to ensure that our vote is counted is nearly impossible for a lot of people.”

Young argued the case for protecting voting rights with Kamala Harris at a White House meeting and is collecting signatures of Navajo leaders to register their discontent with Sinema. She welcomes the prospect of another Democrat challenging her in a primary election one day.

The filibuster, which is not in the US constitution, enables the Senate minority to block debate on legislation. Barack Obama has called it “a Jim Crow relic”, a reference to its long history of thwarting civil rights legislation.

Apart from blocking voting rights legislations, Republicans have used it to block the creation of a 9/11-style commission to investigate the 6 January insurrection at the US this year. Activists regard eliminating the procedure as crucial to other issues including immigration reform and reproductive rights.

In a CNN town hall last month, Biden indicated willingness to “fundamentally alter the filibuster”, adding that it “remains to be seen exactly what that means in terms of fundamentally – on whether or not we just end the filibuster straight up”.

But just as on his economic agenda, senators Joe Manchin of West Virginia and Sinema stand in his way. Both have repeatedly defended the filibuster, with Sinema arguing that it “protects the democracy of our nation rather than allowing our country to ricochet wildly every two to four years”.

Just Democracy, a coalition led by Black and brown organizers, is coordinating with Arizona groups to step up the pressure on her to reconsider.

This includes a psychological thriller-style parody movie trailer, The Betrayal, about Sinema turning her back on people of color in Arizona, ending with: “Now playing in Sinemas near you.” It will be backed by anadvertising campaign in Arizona and run alongside horror content on the streaming service Hulu.

Channel Powe, 40, a local organizer, former Arizona school board member and spokesperson for Just Democracy, said: “We’re going to make it politically impossible for Senator Sinema to continue to stand by the filibuster. In this week of action we are creating a surround sound effect that pushes Senator Sinema on the filibuster. We wanted to share the terrifying consequences of the world that Sinema is enabling.”

Powe added: “Once upon a time, she was a mentor of mine in a 2011 political fellowship that I participated in. I looked up to her. Kyrsten used to be a fierce fighter for the people. But once she got to Congress, she turned her back on the very same people who helped her get her in office.”