In Kyrsten Sinema’s 2009 book, Unite and Conquer: How to Build Coalitions That Win and Last, she described the necessity of working with Republicans so she could “get something done.”

But after months when Sen. Sinema (D-Ariz.) has defiantly snubbed a $3.5 trillion reconciliation package that contains the bulk of President Joe Biden’s plan for tackling climate change, many Democrats think she just may have gone too far.

“Now she’s working with Republicans to get nothing done,” said Sandy Bahr, executive director of the Grand Canyon Chapter of the Sierra Club.

“If she’s not supporting strong climate policy, then she’s definitely out of step with Arizonans,” said Bahr, a veteran environmental activist who has worked for Sinema’s campaigns and who said that, in a state with too little water and way too much heat, voters grasp the need for urgent climate action.

“They get it; they see it; they’re living it,” she said.

Instead, the Arizona Democrat is helping to push through an infrastructure bill that includes little to tackle climate change, only measures to address its impacts. On Thursday, Sen. Joe Manchin (D-W.Va.) said he was in favor of a $1.5 trillion reconciliation package. Then, late Thursday night, House Democrats delayed a planned vote on a roughly $1 trillion infrastructure bill that Manchin and Sinema had helped negotiate, after liberals refused to support it in response to the centrist Senators’ failure to get behind Biden’s reconciliation package.

Sinema and Manchin are the two holdouts in a Senate where every Democratic vote is needed to pass the reconciliation package. And while Manchin’s objections to the spending plan—he has said it costs too much and includes clean energy provisions that are too onerous—may be understandable in a coal-state politician, Sinema’s reasons for withholding her support remain mysterious, even to her Democratic colleagues. 

In a recent interview with the Arizona Republic, Sinema acknowledged that she had “an interest in policies addressing climate change” in the reconciliation plan and in some of  its proposals for “human infrastructure.”

But asked about what she specifically wants and doesn’t want in the reconciliation package, she said, “I don’t make decisions based on other peoples’ actions or other peoples’ behavior. And I don’t engage in hypotheticals or predict outcomes.”

Tiernan Sittenfeld, senior vice president of government affairs for the League of Conservation Voters, said Sinema has a long record of recognizing climate change as a real and urgent problem.

“She has this opportunity to be part of transformational progress for her state and for our country,” Sittenfeld said. “We certainly hope and expect that she will meet the moment and support the package.”

Progressives, in particular, aren’t so sure. The stakes are dire for Democrats and their leader in the White House, whose climate proposal is aimed at cutting greenhouse gas emissions in half by 2030 with a carrot-and-stick approach.

The reconciliation package includes a grab-bag of programs that have been bundled together and separated from the infrastructure bill to avoid the necessity of winning over at least 10 Republican senators. The reconciliation package contains climate provisions to promote clean electricity generation, spark electric vehicle purchases, reduce potent methane emissions and conserve soil. According to one analysis, that’s 1.3 billion metric tons in emissions cuts, just as new international climate talks—the first since the United States rejoined the Paris accord—begin next month.

Maria Nájera, director of government affairs for the regional advocacy group, Western Resource Advocates, said it’s essential for Congress to pass the reconciliation package before Capitol Hill potentially returns to Republican control in next year’s elections and the White House potentially does too in 2024.

Nájera’s group is part of a coalition that’s pressing for $150 billion to be included in the reconciliation package for the Clean Electricity Payment Program, intended to push utilities toward ensuring that 80 percent of the nation’s electricity is furnished by clean energy sources within a decade. She said programs like this are needed to address a climate emergency that Americans are already experiencing.

“It’s only going to get worse,” she concluded. “And, if you’re not actually focusing on turning off the tap [to slow climate impacts], all the buckets in the world aren’t going to help you.”

Eli Zupnick, spokesman for Fix Our Senate, a filibuster-reform advocacy group, pointed out that historical trends suggest Democrats could lose their House majority next year and the legislative opportunities that go along with that power. The onetime Senate staffer added that politicians are determined to avoid letting gridlock and congressional dysfunction get in the way of results that they can brag about to voters.

“I don’t think Sen. Sinema or any other smart politician like her is going to want to go home and just give excuses—they’re gonna want to talk about their accomplishments, about what they got done,” he said. “There’s gonna be a lot of disappointed people across the country if Democrats miss this opportunity [to enact bold climate policy] which could be the last opportunity for a generation.”

Sinema’s potential to derail her party’s agenda prompted one headline writer to declare her a “Democrat Only Republicans Can Love.” Another said the senator’s resistance to progressives is “driving them to the brink.” Meanwhile, Joy Behar, host of ABC’s “The View,” said on Wednesday that Sinema and Manchin “must be brought to task” because they are blocking the Democratic agenda and threatened to be “the ruination of the nation.” She said, “These people are destroying the country in my opinion.”

Recent news reports also have begun to surface about hostility toward Sinema among fellow congressional Democrats. Rep. Veronica Escobar of Texas complained about Sinema’s “lack of transparency that prevents progress” on the spending bills.

And Rep. Ro Khanna of California has been listing his grievances with Sinema in interviews with multiple news outlets: It is “insane” that the Arizona senator won’t say what she likes and dislikes about the reconciliation proposal, Khanna told Axios, unlike Manchin, who made it clear in the press and to colleagues.

“You know exactly where he’s coming from,” Khanna said.

To NPR, he added, “You have no sense of how she plans to get the revenue, you have no sense of what she wants in there, what she’s not for, and that’s what makes it so difficult.” 

And on MSNBC’s The Reidout, he complained, “How can we negotiate and compromise when the other person isn’t even willing to have a starting offer, not just to us, but not to the president?”

In a statement Sinema’s office released Thursday, her spokesman said she has made clear her concerns, including dollar figures, to the White House and Senate Majority Leader Chuck Schumer, CNN reported.

It’s not the first time the Arizona politician has stood apart from her party—she cultivated a reputation as an unpredictable centrist throughout her rise in a GOP-controlled state, pinballing from conservatism to progressive activism and ultimately landing on the bipartisan approach modeled by her political hero, the late Sen. John McCain, the Republican nominee for president in 2008 and a longtime advocate of climate action.

A graduate of Brigham Young University, owned by the ultra-conservative Church of Jesus Christ of Latter-day Saints, Sinema began her political career in Arizona campaigning for Ralph Nader in 2000, leading the Arizona Green Party’s communications on LGBTQ rights and other progressive issues. She is a lawyer and social worker with several advanced degrees, whose political strategy began shifting when she won a seat in the state Legislature in 2004.

Both houses of Arizona’s Legislature have been mostly under the control of the GOP for three decades. The governor’s office also has been occupied by Republicans, except during the tenure of Democrat Janet Napolitano from 2003 to 2009.

Working with Arizona’s dominant political party helped Sinema, in 2018, become the first woman that Arizona voters elected to the U.S. Senate and the first Democrat to win a U.S. Senate seat in 33 years. She is also reportedly the Senate’s first openly bisexual member.

During her Senate campaign, in which she told staff she wanted to be “the next John McCain,” she specifically talked about bipartisan solutions to climate change.

“It’s working together, Republicans and Democrats from these states across the region, that’s how we will find solutions to these challenges,” said Sinema, describing herself as an outdoor enthusiast who wanted to protect the state’s beauty for future generations.

Sinema has pointed to the infrastructure bill that she helped craft as proof that bipartisanship can solve problems. Her congressional website extols the provisions of the bill for water, wildfire, clean energy and grid updates that reduce estimated emissions by about 5 percent. Yet the fact sheets on the site tout the climate friendly accomplishments without using the words “climate change,” a term that many Republicans object to.

Diane Brown, executive director of the Arizona Public Interest Research Group (AzPIRG), sees Sinema’s actions as effective politics in a sharply divided Arizona, which concluded a recount of the 2020 presidential election last week that took more than five months, cost $6 million dollars and ultimately added votes to the Democratic president’s win.

“Sen. Sinema has consistently taken an approach focused more on public policy than partisan politics,” said Brown, whose group supports the senator.

Others contend that Sinema’s effort to find that elusive common ground in the U.S. Senate has caused her to lose her sense of direction.

She was absent for the vote to create the Jan. 6 insurrection investigation commission and opposed the $15 minimum wage. “She’s made it pretty clear that she enjoys being the enemy of the left, she thinks that is good for her politically in Arizona,” said Tré Easton of the Battle Born Collective, which advises grassroots organizations that sprung up during the Trump era. “And, to the extent that the left is angry with her, that’s probably her political sweet spot.”

The League of Conservation Voters said Sinema cast pro-environment votes only 62 percent of the time in 2020 for the second lowest score among Senate Democrats and just above Manchin’s 54 percent; Democratic senators overall averaged scores of more than 90 percent.

Then-Congresswoman Sinema was one of seven House Democrats in 2018 who voted with the GOP majority in favor of a non-binding resolution denouncing carbon taxes. As a senator, she voted to confirm President Donald Trump’s appointees in key environmental positions, while supporting a resolution to allow his rollbacks of environmental regulations and opposing the Green New Deal.

National groups are stepping up their efforts targeting Sinema’s politics, too.

R.L. Miller, founder of California-based Climate Hawks Vote, pointed out that Sinema was named this summer as one of the 11 senators who Exxon regards as central to its efforts to derail national climate legislation. She said Sinema has failed to make positive contributions to climate policy and could face an intra-party challenge for reelection because she’s refusing to support the Democratic agenda at this crucial time.

“I really think that the Democratic base in Arizona is so angry with her that it’s gonna kill off her career,” said Miller, who said progressives have already begun considering prospects to line up a strong primary challenger for Sinema in 2024.

“We’ve seen this movie before,” said Miller. “I just don’t know whether it ends badly for her or for all of us.”

While the Senate has struggled with the reconciliation package, a chapter of the youth-led Sunrise Movement based in Tempe has been protesting outside Sinema’s office even though it is unoccupied because of the Covid-19 pandemic.

“Reconciliation is one of the best opportunities to have any climate legislation, or climate spending, in the next two years,” said organizer Casey Clowes.

“We’re posing the question to Sen. Sinema: ‘Which side are you on? On the side of constituents who are trying to solve and survive the climate crisis, or on the side of the fossil fuel executives?’”