One of the Democratic lawmakers most crucial to the party’s social spending bill is also one of the hardest to read. Sen. Kyrsten Sinema (Ariz.) is frustrating some of her colleagues and constituents by withholding her support but not being vocal about what elements of the bill would win her vote. The New York Times reports that five veterans who have served for two years on an advisory council to her recently quit, calling her “one of the principal obstacles to progress.” And liberal activists have tried to confront her back home in Arizona, in a bathroom, and on planes and in airports.

Sinema is frequently compared to Sen. Joe Manchin III (W.Va.), the other prominent Democratic holdout, who regularly gives news conferences and is relatively direct and forthcoming about what he will and won’t support.

In a 50-50 Senate, Democrats need Sinema and Manchin onboard for any legislation, but particularly this one, which they need to pass through the reconciliation process that allows a simple majority to prevail.

As Democrats are optimistic that they’re nearing a deal all their party’s senators will support, here’s what we can piece together from her very few public comments and reporting about what Sinema expects to see in the measure to get her vote. (Her office says it doesn’t negotiate through the news media and declined to comment.)

She wants to know a lot of details about specific programs. Sinema is almost going line by line in the huge bill to ask specific questions of specific programs, my colleague Mike DeBonis has reported. Sen. Christopher A. Coons (D-Del.) told DeBonis last month that Sinema asked about his proposal for a Civilian Climate Corps aimed at creating jobs while fighting climate change. DeBonis reports:

Sinema, Coons said, wanted to know more about whether the program could be quickly grown to the scale that its supporters envision.
“It’s a perfectly reasonable question,” Coons added. “I spoke up in caucus and said, you know, this is one of the ones I’m working really hard on. And she said, ‘Okay, I need answers to this, this, this and this.’ ”

She wants the House to pass an infrastructure bill to upgrade the nation’s roads. This is legislation that Sinema helped negotiate and that got 19 Republican votes in the Senate. All that stands between this becoming law is a vote in the House of Representatives, but House liberals are holding it up to try to get Sinema and Manchin to come to an agreement on the social safety net bill. As she has slammed liberal Democrats’ hostage-taking as “inexcusable,” she has threatened to do the same, refusing to vote for the social spending bill until the House votes on her infrastructure package.

She wants the social safety net bill to cost much less. Because of a budgetary maneuver Democrats are using to pass this over Republican objections, Democrats actually had to vote on a price tag first. In August, Sinema joined other Democrats in voting for a $3.5 trillion budget resolution, laying the groundwork for the social infrastructure bill, but then she immediately said she wanted it to be less. “[W]hile I will support beginning this process, I do not support a bill that costs $3.5 trillion,” she said in a statement. She told the Arizona Republic she wants to be careful not to increase government spending in a way that raises prices.

She is skeptical about raising corporate or individual taxes. Democratic congressional leaders have insisted that this legislation would be paid for largely by raising taxes on corporations and the wealthy. Sinema, the New York Times reported, has privately told senators that she doesn’t like those tax increases, at least to the degree the rest of the party has been open to.

She is also skeptical of a prescription-drug-pricing measure to help pay for the bill. This, alongside her potential opposition to raising taxes, is a big problem for Democrats. They want to allow Medicare to negotiate lower drug prices, hoping that if Medicare can save money on prescriptions, that’s hundreds of billions the government can pocket to pay for the safety net bill. Politico has reported she’s potentially opposed to that. “She is carefully reviewing various proposals,” Sinema spokesman John LaBombard said. This frustrates Democratic negotiators: The idea polls well with Americans, and without it, Democrats might not be able to expand Medicare to cover dental, vision and hearing, a major priority for Sen. Bernie Sanders (I-Vt.).

Sinema is one of the top recipients in Congress of donations from the pharmaceutical industry, Kaiser Health News reports. That includes about $25,000 from that industry over the summer.

She wants to push for climate change proposals: She has talked about how her state is experiencing drought and wildfires as a result of climate change and indicated she wants to prioritize legislation to help mitigate that and lower carbon emissions. “We know that a changing climate costs Arizonans,” she told the Arizona Republic. “And right now, we have the opportunity to pass smart policies to address it — looking forward to that.”

She also talks about how she’s a former social worker: The implication being, even as she is skeptical of a heavy hand in government overall, she could be open to some major safety net proposals in this bill. The headline policies include universal prekindergarten and paid family leave.

This has been updated with the latest news.