U.S. Rep. Kyrsten Sinema is running for the Senate seat held by Jeff Flake, ending months of speculation about her political future and giving Democrats a top-tier fundraiser with experience on Capitol Hill.

In a video announcing her bid,the Arizona Democrat recounts her upbringing in a family that fell from the middle class into homelessness. She made her way to Congress, Sinema says, with hard work and help from "family, church and, sometimes, even the government."

"I really feel like I have a duty to serve and give back to this country, which has given so much to me," she said in an interview with The Arizona Republic. "Working hard is all I know; it's who I am. I believe I'll be the hardest worker for Arizonans in the United States Senate."

Sinema, who has a reputation as an energetic problem-solver not focused on partisanship, said she intends to make her work on behalf of military veterans and in cutting regulatory red tape for businesses the core issues of her campaign.

"Our nation is facing a lot of problems right now, but we can fix these problems if we work together," Sinema says in the video. "It's time to put our country ahead of party, ahead of politics. It's time to stop fighting and look for common ground."

The announcement echoes her frequent lament that "Washington is broken." But she also brings a relatively slender list of legislative accomplishments in Congress, where gridlock has dominated since Sinema first won her House seat in 2012.

Flake campaign spokesman Will Allison cast Sinema as too liberal for Arizona.

“From her time working on Ralph Nader's campaign to the state legislature to Congress, Kyrsten Sinema has always been out-of-touch with Arizona and she'll do anything to hide her progressive record,” Allison said in a written statement.

A seat in Democrats' sights

Sinema has set her sights on unseating Flake, who is already battling former state Sen. Kelli Ward for the Republican nomination and is trailing the GOP challenger in recent polls. But before that, Sinema faces attorney and community activist Deedra Abboud in the race for the Democratic nomination, as well as political unknowns Jim Moss of Globe and Richard Sherzan of Mesa.

Arizona Democrats, who haven't won a U.S. Senate race since 1988, will have to choose between candidates like Abboud, a novice whoembraces progressive policies, and Sinema, who has won three terms in the House, in part by working with Republicans.

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Democrats nationally see Flake's seat as a key opportunity in an otherwise dreary Senate map for the left in 2018.

Sinema is among the top fundraisers in the House, adding new financial pressure to Flake.

With Sinema vacating her congressional seat, the 9th District is expected to see more Republicans pursuing a seat that is considered competitive on paper but has been hers alone since it was created.

One recent poll suggests she could win the Senate seat. Phoenix Republican consulting firm HighGround Public Affairs found Ward leading Flake by 14 percentage points in the GOP primary and Sinema leading Flake by 8 percentage points in a general-election matchup.

It's a political squeeze similar to the one Sen. John McCain faced in 2015, when he battled Ward on his right and then-U.S. Rep. Ann Kirkpatrick, another moderate Democrat, whom he soundly defeated last year.

Opposed 'Obamacare' repeal

So far this year, Sinema has voted in line with the Trump administration's known preferences 49 percent of the time, according to the website FiveThirtyEight. By that measure, she is the third-most GOP-friendly Democrat so far this year.

By contrast, Flake has voted with the administration 92 percent of the time. Seven of the other 51 Republicans in the Senate have lower marks, including Sen. John McCain of Arizona.

Sinema's proudest legislative accomplishment to date is passage last year of a measure to require the VA to accommodate veterans needing mental health assistance, even if their work involved classified information that needs special handling. It is named for Daniel Somers, a Phoenix Iraq War veteran who said he killed himself after hitting roadblocks with the VA.

SEE ALSO:The congresswoman who grew up in a gas station

Some Democrats have complained that Sinema has been too eager to support law-enforcement bills that would make life more difficult for immigrants. At the same time, she has been outspoken in her support of "dreamers," immigrants brought to the U.S. illegally as children.

While Sinema has frequently supported the current GOP agenda, she did not vote for the health-care reforms that are arguably the most divisive and high-profile legislation of the Trump era.

Sinema has made reforms for VA hospitals and improved economic opportunities for those with military ties a centerpiece of her time in Congress, though the hospital system remains in a state of upheaval more than three years after The Arizona Republic uncovered widespread problems in Phoenix.

Earlier this month, Sinema met with President Donald Trump as part of a bipartisan group of House moderates seeking common ground on issues ranging from accommodating dreamers and enacting temporary measures to stabilize the Affordable Care Act, to sweeping tax changes. Such bipartisan meetings have become a rarity in Washington, and her presence speaks to Sinema's reputation as a Democrat that Republicans can work with.

Sinema co-sponsored this year a bill to better connect business startups with investors by cutting regulatory requirements. That measure is pending in the Senate. A member of the House Financial Services Committee, she is generally supportive of cutting taxes and of the kind of public-private infrastructure plan sketched out by the Trump administration, though she also cites concerns about the government's growing national debt.

TALKING POLITICS: Listen to our Arizona politics podcast, The Gaggle, on Apple Podcasts, SoundCloud, Stitcher or Google Play.

Bipartisan reputation

Sinema has occasionally frustrated Democrats with what she sees as a need for moderation. She has declined to vote for Nancy Pelosi as her party's leader in the House. She also skipped a Tempe rally for Hillary Clinton at the end of the 2016 presidential campaign.

She is friendly with Republicans in the House, including Arizonans like former Rep. Matt Salmon and his successor, Rep. Andy Biggs, both of whom are among the most conservative members of the GOP.

SEE ALSO:Taking a spin class? Sinema could teach you

Sinema frequently co-sponsors Republican bills, enough to make her the third-most bipartisan member of the House and the fourth-most conservative Democrat in the Congress that ended in 2016, according to GovTrack, a nonpartisan organization that monitors congressional activity. She was near the bottom of House sophomores at attracting influential co-sponsors to her own bills, GovTrack found.

Sinema's bipartisanship extends to social media, where she routinely passes along birthday wishes to colleagues in both parties.

But the National Republican Senatorial Committee signaled in a statement Thursday that Republicans will attempt to cast Sinema as “extreme."

“Kyrsten Sinema has more in common with the failed, radical leadership of Nancy Pelosi than she does with Arizonan families, and her track record of voting in lockstep with Washington Democrats will haunt her uphill campaign for Senate," NRSC Communications Director Katie Martin said in a statement.

A prolific fundraiser

One thing that is not expected to be a problem for Sinema is money.

She is one of the more prolific fundraisers in Washington. Through June, she had amassed $3.2 million in campaign cash, which was one of the largest sums in the House and topped the $3 million that Flake had raised by then.

SEE ALSO:Handicappers lower GOP chances to hold Flake seat

Her fundraising at least briefly posed a problem earlier this year when The Republic noted that she accepted contributions from the embattled founders of Backpage.com, a website accused of knowingly accepting ads offering sex with underage girls.

Sinema eventually gave the money, about $53,000, to a charity to combat sexual abuse, but only after other charities rejected what they viewed as tainted cash.

Flake and McCain helped keep pressure on Backpage this summer by introducing a bill to make it easier to prosecute online publishers aiding in sex trafficking.

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