Five veterans on Sen. Kyrsten Sinema’s advisory council resigned, accusing the centrist Arizona Democrat of being “one of the principal obstacles to progress” because she refuses to back key provisions of President Biden’s agenda that “support our veteran community and protect the very heart and soul of our nation.”

In a letter, first reported by the New York Times, the veterans said they could no longer stand by Sinema as she continues to oppose portions of the president’s multitrillion-dollar domestic policy agenda. They also criticized her opposition to abolishing the filibuster, a tool Republicans are using to block voting rights legislation.

The veterans said Sinema is hanging her constituents “out to dry” and accused her of “answering to donors rather than your own people.”

“We shouldn’t have to buy representation from you, and your failure to stand by your own people and see their urgent needs is alarming,” they said.

The group also took issue with her lack of support for negotiations on reducing the cost of prescription medication, which they said contravenes her campaign promises.

“These are not the actions of a maverick,” they said, referencing the late Sen. John McCain (R-Ariz.), Sinema’s predecessor and self-described role model.

In response to the letter, Sinema lamented the veterans’ departure from her advisory council but said she appreciates “their diverse views [and] contributions to legislation.”

“While it is unfortunate that apparent disagreement on separate policy issues has led to this decision, I thank them for their service and will continue working every day to deliver for Arizona’s veterans who have sacrificed so much to keep us safe and secure,” she said in a statement.

Army veteran David Lucier, a Green Beret, was one of the five members of the council who quit. He told The Washington Post that he and other veterans had been working with Sinema for years, starting when she was a representative in the Arizona legislature. They had collaborated on successful programs, he said, including one that offers in-state tuition for veterans.

“So our relationship goes way back, and it was based on trust, it was based on important issues to us,” Lucier said. Now, however, the group “felt that our voices weren’t being heard, action was not being taken on the issues that we raised, and it became very frustrating, and the frustration turned to anger. And I think this is the natural outcome of the deterioration of that relationship.”

Portions of the letter are being used in a new ad by the progressive veterans group Common Defense. The ad will air in Phoenix and Tucson and calls on Sinema to support Biden’s economic agenda.

“Sinema considers herself to be kind of a maverick in the form of John McCain, and I think by making this statement, veterans are showing that it takes a lot more than just words to be a real maverick, or be a real leader,” said Naveed Shah, a U.S. Army veteran and Common Defense’s political director.

A spokeswoman for Sinema said the senator regularly meets with members of her veterans’ advisory council to discuss veterans issues and other topics. The five veterans who quit the council had been working with Sinema since 2019. Their term was set to end in December.

Lucier, the Green Beret, said he was particularly bothered by Sinema’s support for upholding the filibuster, even if it stands in the way of advancing voter rights. Lucier, who fought in Iraq, said veterans “fought and died and bled” for people’s right to vote in the Middle East, and he couldn’t fathom that a Democrat from his home state would stand in the way of easing access to vote for other Americans.

“We’re looking at our rising star in Kyrsten Sinema, and she’s very lackadaisical when it comes to voting rights,” he said. “That’s a horrible place to be.”

The veterans’ resignations add to the frustration many in Sinema’s circle have felt in recent weeks as the centrist Democrat continues pushing against key provisions in the Biden agenda despite compromises from both the president and the progressive wing of the Democratic Party.

Sinema has received plenty of criticism from constituents in her politically competitive state, with protesters confronting her in airports, on airplanes and in bathrooms. The bathroom incident, in particular, drew rebuke from the senator, who called it “wholly inappropriate.”

Still, because Democrats hold a slim majority in the Senate, the Biden agenda cannot afford to lose the support of Sinema or fellow centrist Sen. Joe Manchin III (D-W.Va.). Unlike Manchin, however, Sinema is withholding her support while not sharing which specific elements of Biden’s domestic policy bill she actually wants to see in a final version. Manchin is known for regularly communicating what he will and won’t support.