Kyrsten Sinema says she is worried about inflation. The U.S. senator from Arizona says new tax hikes could harm businesses still struggling in the wake of the pandemic. She doesn’t think the solution is always more federal spending, and she still won’t scrap the Senate’s rules to advance more of her own party’s agenda.

And no matter what her critics insist, the first-term Democrat — a centrist with a penchant for silence even in a time of boisterous politics — maintains that her views shouldn’t come as a shock to anyone.

“I’m always surprised when people say, ‘Oh, she’s an enigma,’” said Sinema, who spoke with The Washington Post on Thursday in a wide-ranging half-hour interview. “I’m, like, not at all, actually. I’m very straightforward about what I believe in and why I’m doing what I do.”

For Sinema, 45, the rare moment of public reflection illustrates a senator newly emboldened. Already a power broker in a chamber where Democrats cannot afford to lose her vote, she has increasingly embraced her role as a countervailing force in the battle over President Biden’s agenda — frequently putting her at odds with lawmakers in her own party.

Sinema’s approach politically has paid early dividends: On Monday, the president signed into law an approximately $1 trillion plan to improve the nation’s infrastructure that she helped negotiate over the past year. But her philosophy also has generated its fair share of internal conflict. The skirmishes have been fiercest around Democrats’ second package to overhaul the country’s health-care, education, climate and tax laws, which Sinema has sought to scale back dramatically.

Speaking Thursday in her subterranean Senate hideaway — a pink-walled office adorned with small ornaments honoring her Arizona roots — Sinema laid out some of her thinking. She argued for delivering more targeted federal aid than some Democrats originally had envisioned as part of their first bill, once valued at $3.5 trillion. With inflation spiking in October, Sinema added that she hopes it “helps people understand why I have been concerned about high levels of spending that are not targeted or are not efficient and effective.”

Sinema also sent mixed signals a day before the House adopted a retooled, roughly $2 trillion tax-and-spending plan. She noted it differs from the blueprint that Biden had worked out with centrists weeks earlier, but she did not say what, if anything, she might change.

“So, that’s not the agreement the president put out in his framework several weeks ago,” the senator said. “While I’m not going to comment on what’s happening in the House at this moment, I can just refer you back to the comments I made when the president put out his framework. … I’m looking forward to working with him to get this done.”

In staking such positions, Sinema’s politics and style often have drawn the ire of other Democrats, especially liberals, some of whom see her efforts as a threat to their political ambitions in a time of narrow congressional majorities. But Sinema on Thursday rejected the notion that she had become an outlier in her own party, saying she takes positions that reflect the desires of her voters back home.

“I do not feel that at all,” she said. “And it’s because I live in Arizona … and folks are regular, everyday people in Arizona. Interestingly, people in other parts of the country don’t lead with their political beliefs.”

The week nonetheless continues a political transformation for Sinema, a social worker by training who rose through the ranks of Arizona government before arriving in Washington in 2012. First as a junior member of the House and now as a swing vote in the Senate, she increasingly has sought to cut a moderate profile, reflecting the political temperament of a southwestern state that before Biden had not voted to send a Democrat to the White House since 1996.

The approach served Sinema well over the course of a career in which she often served in the political minority. Now, though, the senator belongs to the party in charge — and repeatedly has faced criticism for her centrist views.

The blowback intensified in June, when she took to the pages of The Post to reiterate her belief that the narrowly divided Senate should maintain the filibuster, which means 60 votes are required for most legislation. Republicans since then have used the threshold to stymie Democratic efforts to tackle priorities including voting rights, which Sinema on Thursday said is still an insufficient reason to do away with the practice.

“My opinion is that legislation that is crafted together, in a bipartisan way, is the legislation that’s most likely to pass and stand the test of time,” she said. “And I would certainly encourage my colleagues to use that effort to move forward.”

Liberal-leaning Democrats in recent months also have seen her more as a foe than a friend on economic policy, someone intent on reeling in their ambitions in a rare moment when they control all the levers of power in the nation’s capital. Some in the Arizona Democratic Party previously have threatened to censure her. Other national party figures have raised the prospect of a primary challenge when she is up for reelection in 2024.

Other Democrats have openly vented frustration about Sinema’s tendency to negotiate with a very small circle of other lawmakers and administration officials. She defended her publicly opaque nature, saying “building trust” and “protecting the work” was the most likely path toward a deal.

Sinema pointed to the recently signed infrastructure law as validation of her style and approach.

“I would suggest that the proof of that method is what we’ve been able to deliver,” Sinema said.

In Sinema’s telling, the road toward a long-sought deal began in March, well before she and other Democrats and Republicans had gone public with their efforts to resolve one of Washington’s most intractable policy fights. She huddled at first with Republican Sen. Rob Portman (Ohio), then a widening cast of fellow moderates, in a process that soon came to involve Biden.

Biden’s first efforts to broker a bipartisan deal with the Senate would ultimately fail. But she recalled that at one point — as he was still negotiating with senior Republicans — the president phoned Sinema to tell her, “Please keep working on this effort.”

“I said, ‘I’m going to,’” Sinema said, later adding about the negotiation process more broadly: “No one tells me what to do.”

The resulting $1.2 trillion measure signed into law this week aims to improve the nation’s roads, bridges, pipes, ports and Internet connections. Many of the fixes may take years to implement, though Sinema stressed Thursday that Americans should see benefits sooner, since lawmakers tried to focus much of the funding on existing federal programs that repave thoroughfares and replace water systems.

“When we were drafting the bipartisan infrastructure law, we specifically took care to include shovel-ready projects that would be ready to start moving as quickly as possible,” Sinema said.

Attending the signing ceremony at the White House on Monday, Sinema said that at one point she waved down Mitch Landrieu, who Biden just appointed to oversee implementation of the infrastructure law. She recalled that she urged him to move “very quickly to start down the road of efficient and effective implementation.”

Sinema similarly has been critical of Democrats’ plans to spend additional sums to advance the rest of the party’s agenda — from an expansion of Medicare to new tax benefits chiefly targeting low-income families. Unlike the infrastructure law, which lawmakers adopted on a bipartisan basis, Democrats aim to secure the second package using a legislative maneuver that allows them to sidestep unanimous GOP opposition.

That process, known as reconciliation, initially troubled Sinema. She joined Democrats in August to take the first procedural step that allowed them to pursue the bill, crafted chiefly by Sen. Bernie Sanders (I-Vt.). But she also made clear she would seek future cuts, expressing particular concern about the deficit.

The process to whittle down the bill ultimately spanned months, at times pitting Sinema and her centrist colleague, Sen. Joe Manchin III (D-W.Va.), against liberals including Sanders, who believed they had an election mandate to spend more. Explaining her position Thursday, Sinema cited her own experiences with poverty as a child.

“In addition to my own training as a social worker for a number of years before I entered into politics,” she said, she “grew up in very difficult financial circumstances. So I do understand the importance of having a helping hand when families need it.”

But, Sinema added, her focus with the tax-and-spending plan had been on “creating an economic climate that provides opportunity for folks to become financially independent.”

Sinema also argued excessive spending threatened to compound the troubles with inflation.

“The recent numbers on inflation are not a surprise,” she said. “We knew this was coming. And not everyone has paid attention to it or thought about it, but we’ve seen it coming. It’s been coming for some time.”

Many liberals argue that their spending package is actually counter-inflationary, easing Americans’ financial burdens. Others pilloried Sinema for months for not being more forthcoming about her views, choosing instead to remain silent about negotiations with vast economic import. That had the effect of delaying work on Biden’s broader agenda, which for months languished among intraparty battles on Capitol Hill.

Sinema disagreed that she had been secretive. In June, she said, she made clear to the White House and fellow Senate leaders that she would not support a key element of their initial plan — an effort to raise tax rates on individuals and businesses. Her stance broke with Biden, who had wanted to repeal the tax cuts instituted in 2017 during the Trump administration.

Sinema voted against the Trump tax cuts that year as a House member. But she supported unsuccessful legislation in September 2018 — amid a heated Senate campaign for the seat vacated by Sen. Jeff Flake (R-Ariz.) — that would have made the individual rate cuts in the tax law permanent.

“In the context of our negotiations, I am always someone who is prepared, upfront — I have my spreadsheets — and I am always very direct in my conversations,” she said of her position on taxes in the spending bill this year. “So this is something that we’ve been talking about for quite some time.”

Sinema said her goal had been to ensure that any revenue-raising measures in the bill are focused on “maintaining American competitiveness and ensuring that businesses of all sizes in America, and particularly in Arizona, have the ability to grow and to compete.”

For some Democrats, Sinema’s approach has squandered a rare opportunity to advance a wide array of policies that they have been promising voters for years — especially entering midterm elections in which they are at risk of losing their majorities. The senator herself, however, said she views the political moment differently.

“I don’t spend a lot of time thinking about that kind of grand talk,” Sinema said. “What I think about is: What are the folks in my state hungry for? What do they need? How can I make their lives a little bit better? How can I make government less of a problem in their life? And what are the things that I can do today to help solve that? And, you know, I think it works.”