WASHINGTON (AP) — Neera Tanden has delighted in labeling Senate Majority Leader Mitch McConnell as "Moscow Mitch"; in the wake of the acrimonious vote to confirm Supreme Court Justice Brett Kavanaugh, she cuttingly dismissed Maine Republican Sen. Susan Collins as "the worst."

And as Democrats wrestled with the 2016 loss, Tanden tweeted her takeaway in a dig on former first lady Michelle Obama's often-quoted political truism: "One important lesson is that when they go low, going high doesn't ... work."

Tanden, who is president of the Democratic-leaning Center for American Progress and now president-elect Joe Biden's choice for budget director, has spent years as a partisan combatant willing to go low against both Republicans and left-leaning critics of her former boss Hillary Clinton. Now some of those she's bruised along the way see her upcoming confirmation as a chance to hit back, making her perhaps Biden's most controversial staffing and Cabinet decision yet.

Some Republican leaders have declared their opposition to Tanden — drawing a new red line over Twitter etiquette after years of ignoring President Donald Trump's tweets. Some progressives, meanwhile, see Tanden's nomination as a test of whether the left will challenge Biden, who ran as a moderate, over funding for social programs.

"If she sails through without a challenge (from the left), it speaks badly for the progressive wing's willingness to challenge Biden on anything," said David Sirota, a former speechwriter for leftist Vermont Sen. Bernie Sanders who also worked at the think tank under Tanden.

Sanders has not commented publicly on Tanden's nomination, but other liberal senators including Elizabeth Warren of Massachusetts and Sherrod Brown of Ohio have expressed their support.

Tanden would be the first woman of color to lead the powerful Office of Management and Budget. Friends and allies say that the fuss over her online persona is a distraction from her credentials and deep experience with large-scale policy making. That includes her roles in helping Clinton develop her health care plan in 2007 and later as a senior adviser that helped craft "Obamacare."

"She is a policy wonk first and foremost," said Lindsay Hamilton, a former chief of staff to Tanden at the Center for American Progress.

On Friday, Biden tweeted his support, calling her "a brilliant policy mind with experience across government" and saying "above all, she believes what I believe: a budget should reflect our values."

Tanden, 50, has said her values reflect personal experience with the government programs she would play a key role in supporting.

The child of Indian immigrants, her parents divorced when she was five and her mother spent two years on government support, food stamps and Section 8 housing vouchers in the suburbs of Boston before eventually getting a job as a travel agent.

"I'm here today because of social programs, because of budgetary choices, because of a government that saw my mother's dignity and gave her a chance," Tanden said last week, as Biden announced the nomination. The experience gave her a belief in the ability of government to "pull families back from the brink," she added. Biden's team declined to make Tanden available for an interview.

The first wave of Republican criticism of Tanden mentioned none of her professional or personal experience, instead focusing on her aggressive Twitter hand.

Tanden's rhetoric online was "filled with hate & guided by the woke left," Arkansas Republican Sen. Tom Cotton said. Republican Sen. John Cornyn called Tanden "radioactive" and a spokesperson for the Texas senator has said she "stands zero chance" of being confirmed if the GOP holds the Senate. (Democrats need to win both of next month's runoffs in Georgia to take control of the Senate.)

Democrats have been quick to point out the hypocrisy in Republicans' focus on Tanden's harsh posts. Most Senate Republicans have spent years backing President Donald Trump as he hurled personal insults — "horseface," "phony," "slob" — at opponents, stoked racial tensions and pushes falsehoods on Twitter.

Tanden has long been close to Hillary Clinton, serving as an East Wing aide to the then-first lady during President Bill Clinton's administration. She would go on to serve as a top staffer in Clinton's Senate office, policy director during Clinton's unsuccessful 2008 campaign and as an outside adviser to Clinton's 2016 campaign for the White House.

Tanden, who referred to herself as a "loyal soldier" for Clinton in a private email made public by WikiLeaks, aligned herself with Clinton early and stuck close to her through much of the last two decades.

Jim Kessler, a former policy director in the office of New York Democrat and Senate Minority Leader Chuck Schumer, said he first got to know Tanden more than 20 years ago when she called him to get a primer on New York politics as Clinton launched her first Senate campaign.

"She was a sponge," recalled Kessler. "It's not easy being an outsider and that was not a simple race for Hillary. She was a big part of the reason that Clinton was successful."

After Clinton was defeated by Obama in the 2008 Democratic primary, Tanden joined the Obama campaign and went on to work as a top aide in Obama's Department of Health and Human Services as he put together his signature health care reform.

Tanden left the agency in 2010 to become chief operating officer at CAP, a longtime stronghold of Clinton loyalists.

It's not just Republicans who have a beef with Tanden; her expected nomination shines a light on lingering divisions inside the Democratic Party.

Tanden clashed frequently online, and occasionally in person, with supporters of Sanders, the progressive standard-bearer during his bitter primary battle with Clinton in 2016 and again during his fight against Biden this year. Last year, Sanders wrote an open letter accusing CAP under Tanden's leadership of playing a "destructive role" in the process. Calling out Tanden by name, Sanders said the think tank had a pattern of calling for Democratic unity but then "maligning my staff and supporters and belittling progressive ideas."

Tanden has also previously endorsed cutting entitlements such as Social Security and Medicare — something the Sanders' wing of the party regards as a red line, but a position that Biden himself has held at different times.

Sirota, who now publishes the political newsletter The Daily Poster, said the smoke over Tanden's online persona obscures the true debate among Democrats over her policy choices.

"In a rational political world, that would be the central issue regarding her nomination," he said.

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