Samantha Power

On November 5, Samantha Power took to Twitter to denounce Bashar al-Assad, the Syrian president. “The US view of Assad is unchanged,” wrote the new US ambassador to the United Nations. “A man who gasses his people, Scuds his people & terrorises his people does not deserve to govern those people.”

The tweet revealed a great deal about Power, at 43 the youngest person to hold the post at the UN, which also comes with a seat in the US cabinet. Any remaining Twitter-sceptics would be impressed at the concise and punchy message the one-time Pulitzer Prize-winner managed to pack into 140 characters. (It helps when you have one of the world’s most imposing Twitter handles: @AmbassadorPower.)

The tweet also captured the fierce strain of moral indignation that has quickly transformed the Irish-born Power from freelance war correspondent in Bosnia to one of the most influential intellectuals of her generation for her work on American complicity in 20th-century genocide, an iconic figure for younger women interested in international affairs, and America’s No 2 diplomat.

Yet her verbal volley against the Assad regime, at a time when US policy towards the Syrian calamity seems in disarray, also highlighted the central question that hangs over Power as she tries to make her imprint on foreign policy. In a deeply cautious administration that seems focused on nation-building at home and on hard-nosed calculations of national interest abroad, is she anything more than a token voice pushing the cause of humanitarian intervention?

“It is one of the most heartbreaking situations I have seen in my lifetime,” she says of the Syrian civil war, whose death toll has surpassed 115,000.

It is quite a career for someone who until her early twenties wanted to be a sportswriter. Power was born near Dublin, and her first real passion was baseball. It became her connection to American life when she moved to Pittsburgh at the age of nine and later to Atlanta, where she went to high school. After she won a Pulitzer Prize for her 2003 book on genocide, A Problem From Hell, she was invited to throw the opening pitch at Fenway Park, the legendary home of the Boston Red Sox, to whom she had become devoted while studying at Harvard. Accustomed to presidents and film stars throwing weak pitches into the dirt, the organisers suggested that she might like to start from nearer the catcher. But she insisted on going to the top of the mound. The pitch was not a huge success, yet the memory stuck. “Apart from the birth of my two kids and my marriage, it was the proudest day of my life,” she says.

Her head was turned from sports journalism, however, by the searing images from the civil war in Bosnia. She moved to Sarajevo, where she wrote articles for The Boston Globe and The Washington Post, and gradually became obsessed by the notion that western governments – particularly the US – should take action in the face of mass suffering and atrocity. In between getting a law degree and directing Harvard’s Carr Center for Human Rights, she spent six years researching her book on why the US has so often looked the other way, a period of her life she described as “all genocide, all the time”.

John Prendergast, a former Clinton administration official and long-time Africa activist, travelled with Power in Darfur in 2004, during the height of the atrocities committed by militias backed by the Sudanese government, which she reported on for The New Yorker. “Samantha demonstrated a level of relentlessness in pursuit of the truth that I had never before witnessed in anyone, sometimes at great personal risk,” he says. “Having someone like that in the cabinet of an American administration is a potential game-changer.”

These days Power juggles a very different set of challenges, mixing her job at the UN with the demands of two young children, Declan, four, and Rían, who is not quite two. Speaking in November at an event in Washington organised by Politico magazine, she blushed at being described as a “poster child for the ‘lean-in’ generation”. Power replied: “I am happy if I can read them their story before bed without screwing up the negotiation the next day.”

Power is a political outsider who has been an Obama insider from the start. Barack Obama, then senator, called her after reading A Problem From Hell. At a dinner in 2005 they clicked – both are earnest Harvard law graduates – and she joined his congressional staff.

When Obama became president, Power moved with him to the White House as director for multilateral affairs and human rights at the National Security Council. (She spent some time on the campaign team but had to stand down during the Democratic primaries in 2008 after she was quoted in The Scotsman newspaper describing Hillary Clinton as a “monster”.) It is something of an old trope that young idealists join government and are quickly outmanoeuvred by the old, cynical hands. By Power’s telling, however, one of the most eye-opening aspects of working in the White House is the influence one staffer can have if they prepare well. “It is surprising how a single meeting and the whole direction of policy can be turned by one individual and a single oral intervention,” she says.

She was one of the White House officials who persuaded Obama to intervene in Libya – against the advice of his secretary of defence Robert Gates – when Muammer Gaddafi’s forces were threatening a massacre in Benghazi. She was the driving force behind the creation of Obama’s Atrocities Prevention Board, designed to provide warnings about looming threats. Tommy Vietor, who worked with Power in both Senator Obama’s office and the White House, says she was an effective bureaucratic operator.

“People think of her as a moral conscience, which is true,” he says. “But they forget she also spent a lot of time studying how governments respond to this type of crisis. She knows the system well.”

During the build-up to the 2011 referendum in Sudan that led to the creation of South Sudan, when the Khartoum government was threatening to block the process, Vietor says Power played a large role in getting the US to push for the vote. “She knew what aid could be accessed, what sanctions had been imposed and where the diplomatic leverage was. Her expertise was critical.”

Despite her reputation as a firebrand, she has shown an ability to mouth the sort of political bromides that nurture Washington careers. Her confirmation hearing in July was less the appearance of a fresh new voice defending human rights and more of an experienced political professional. She denounced discrimination at the UN against Israel and promised to “work tirelessly to defend it”.

“This country is the greatest country on earth,” she told the senators. “I would never apologise for America.” After the hearing, the journalist David Rieff complained that Power’s “confident, self-righteous anger” had given way to “an early middle-aged apparatchik whose willingness to pander to her interrogators seemed to know no bounds”.

If A Problem From Hell made her career, it is also a cross Power has to bear, a series of stark judgments against which to assess her performance now. In the book she argues that in the face of mass atrocities, “American leaders did not act because they did not want to”. Perhaps the most famous passage concerns the genocide in Rwanda and the reaction of Susan Rice, then a White House official and now Obama’s national security adviser (and Power’s predecessor at the UN). “I swore to myself that if I ever faced such a crisis again, I would come down on the side of dramatic action, going down in flames if that was required,” Rice told Power.

This is the baggage Power now carries with her as one of the principal US voices on the Syrian civil war. The humanitarian disaster is accelerating rapidly, with as many as five million people driven from their homes by the fighting. Disease is also spreading, including an outbreak of polio.

Against this backdrop, the US response has been criticised for vacillation. The administration announced earlier this year that it would begin arming moderate parts of the opposition but it has done little, fearful its weapons will end up with al-Qaeda sympathisers. Obama threatened to bomb the regime after the August chemical weapons attack but, when Congress appeared likely to reject the plan, he opted instead for a Russian diplomatic initiative to get rid of the chemical weapons. (The proposal became a baptism of fire for Power at the UN, with two weeks of intense negotiations with her wily Russian counterpart Vitaly Churkin.) The president first called on Assad to step down as far back as 2011 but the Syrian leader still seems firmly in control, adding to the sense of US impotence.

The Syria debate has highlighted the gap between Power’s humanitarian worldview and that of Obama. The president was elected to end wars, in Iraq and in Afghanistan, not to start new ones. At his UN speech in September, Obama laid out a more modest path for US intervention, a reflection of “our hard-won humility” from the missteps of the past decade. Iran and Israeli-Palestinian peace would be US priorities in the region: Syria would not.

Power is not the liberal hawk she is sometimes made out to be, supporting military interventions at every looming disaster. She was against the Iraq war, for instance. But last year, she was one of the officials arguing for a more decisive American role in trying to influence the outcome of the civil war. She believes the Syrian situation to be the “singular moral and strategic challenge of our time” and still sees it in terms of an “Arab spring” struggle between dictator and oppressed, despite the appearance of thousands of jihadis among the opposition ranks.

“If anything, the recent success of extremists accentuates the argument to invest body and soul in trying to find a way forward,” she says. “People did not set out to trade a dictator for being under the control of terrorists.”

Yet, aware that she will be accused of selling out her earlier self, she defends her writings beside current US policy in Syria. The point of A Problem From Hell was not always to send in the marines, she says, but to use all possible means to try and prevent atrocities, including diplomacy, sanctions, arms embargoes and the UN.

“What people forget about President Obama’s response to Syria is that he has deployed literally every tool in the box short of going to war in Syria,” she says. As the Syrian conflict drags on, it is an argument she is likely to find herself presenting many times over the next three years at the UN.