WASHINGTON, Sept 30 (Reuters) - Kyrsten Sinema is the recent recipient of an honor that U.S. Senate colleagues more loyal to President Joe Biden's agenda have never received - three invitations to the White House in just one day.
The Arizona Democrat's private huddling this week with Biden and his aides comes as her opposition to the size of a $3.5 trillion social spending proposal has become a key obstacle to Democratic efforts to lock down support for one of the pillars of the president's domestic agenda.
The spending bill seeks to reduce inequality by enhancing access to healthcare and education, while taking steps to tackle climate change. Democrats propose paying for it by raising taxes on big corporations and wealthy Americans.
But Sinema and fellow Democratic Senate moderate Joe Manchin of West Virginia say the bill's price tag is too high, imperiling its prospects in the evenly split chamber where Democrats are trying to pass it through a "reconciliation" process that would not require Republican support.
A spokesperson for Sinema did not respond to multiple requests for comment. In a statement in July, Sinema said: "I do not support a bill that costs $3.5 trillion," promising to "work in good faith to develop this legislation" with her colleagues and the administration.
On Wednesday, the White House would only go so far as to say that "our sense is she does" want a bill to pass.
Asked for more specifics, such as how much Sinema was willing to spend, White House press secretary Jen Psaki said she would not detail negotiations publicly.
Still, Sinema may be the best chance the White House has at striking a deal, administration officials and allies said.
The 45-year-old first-term senator and former social worker was a key figure in reviving talks over Biden's $1 trillion bipartisan infrastructure bill. Once presumed dead, that deal passed the Senate last month with 19 Republicans voting yes.
Its passage in the Democratic-controlled House of Representatives is now complicated by disputes between moderates and progressives over the larger package.
Sinema's seat in the Senate is not up for grabs until 2024, the same year Biden might seek re-election. Still, several liberal groups have already suggested they would back a primary challenge against her for not backing their priorities.
The Arizona state Democratic Party overwhelmingly passed a resolution on Saturday that criticized Sinema for her opposition to eliminating the filibuster to more easily pass legislation blocked by Republicans and for her stance on the Biden spending bill.
Adam Kinsey, a director at Uplift Campaigns, an Arizona-based progressive Democratic consulting firm, said Sinema does not care about the state party reprimanding her.
"She really believes that she can be a dealmaker," he said.
In Arizona, which went for Biden in 2020 after backing Republican former President Donald Trump in 2016, independence is prized, local political operatives said. Its former longtime senator, the late John McCain, was a self-styled maverick Republican.
"She is concerned that if she joins this massive spending bill, she will face serious opposition from a Republican," said Charles Coughlin, chief executive of the Arizona political strategy firm Highground. "She actually polls better among Republicans than Democrats, which is very odd but helps explain her motivations."
Based on a GovTrack analysis of her 2020 voting track record, Sinema is the most conservative-leaning of any Democratic senator, and further to the right than independent Angus King of Maine, who caucuses with the Democrats.
Sinema has also reaped campaign donations from her pushback on Biden.
In April, the U.S. Chamber of Commerce, the largest business lobby group in the country, said it was donating to Sinema and Manchin because they were working with Republicans and opposing some of Biden's policies.
Biden's legislative difficulties may be deeper, however, than any one senator.
A larger group of Democratic caucus members has privately expressed concern to senior Democratic lawmakers and the White House about the 2022 congressional elections in which the party's control of both chambers is at stake, according to people familiar with the matter.
Many of those members expect it will be hard to sell a spending package back home that is so big and unwieldy, even if its individual components are highly popular.
Nodding to such concerns, Building Back Together, a group started with the White House's blessing to push Biden's agenda, released polling on Wednesday reassuring Democrats in 48 battleground districts that voters would reward them for backing a "robust" legislative package that lowers the cost of essentials like healthcare, while raising taxes on corporations and the rich.
Democrats who served when Barack Obama was president recall that the 2010 Affordable Care Act, popularly known as Obamacare, included components favored by most Americans but was initially unpopular in the face of solid Republican opposition.
Later that year, Democrats lost their House majority. Biden was Obama's vice president.
A deal with Sinema does not guarantee success for Democrats. Reducing the overall ambition of the spending package would leave a bad taste for liberal Democrats and could derail House passage of the infrastructure bill, expected to come up for a vote on Thursday.
"We knew it would be a compromise, and that's exactly what it is," said Psaki. "We don't have the luxury to be frustrated around here."
Reporting by Jarrett Renshaw and Trevor Hunnicutt; Editing by Heather Timmons and Peter Cooney
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