Barack Obama insisted that “the buck will stop with me” when he dismissed doubts yesterday over how a heavy-weight “team of rivals” that includes Hillary Clinton and a Republican Defence Secretary can work in harmony.

Presenting half a dozen nominees for senior national security posts, the President-elect said that the “strong personalities and strong opinions” that he had brought together would ensure vigorous debate, even disagreement, in the White House.

“But understand – I will be setting policy as President,” he added. “I will be responsible for the vision that this team carries out, and I expect them to implement that vision once decisions are made.”

On a stage draped with American flags in Chicago, Mr Obama was flanked by Mrs Clinton, the nominee for Secretary of State, whom he described as “my dear friend”; Robert Gates, the Defence Secretary, who is being asked to stay on at the Pentagon; and James Jones, an independent-minded former general lined up to be his National Security Adviser.

Along with Janet Napolitano, Eric Holder and Susan Rice – chosen for roles as Homeland Security Secretary, Attorney-General and United Nations Ambassador – it is a visibly diverse team containing three women, two black people and a Republican.

Mr Obama declared: “This is the team that we need to make a new beginning for American national security. Together, as one nation, as one people, we can shape our times instead of being shaped by them. Together, we will meet the challenges of the 21st century not with fear, but with hope.”

Hanging an “under new management” sign over US foreign policy, he described how his administration, facing global upheaval and unfinished wars, would not only use military, diplomatic or economic might to pursue its interests but would also lead through “the power of our moral example”.

He provided scant detail on policy, except for reiterating a determination to tackle terrorism after the attacks in Mumbai last week and his belief that combat troops can be withdrawn from Iraq within 16 months, subject to advice from military commanders.

Instead the press conference was dominated by questions about his relationship with Mrs Clinton or the often bitter language with which she and he had attacked each other’s foreign policy credentials in the Democratic primaries this year.

“During campaigns or during the course of election season, differences get magnified,” replied Mr Obama, who accused reporters of “having fun” by seeking to stir up past acrimony.

He preferred to dwell on the “core values” he shared with his former rival. “I have always admired Senator Clinton,” he said. “I have always believed that she is tough and smart and disciplined.”

Predicting that she would be an outstanding Secretary of State, he added: “And if I didn’t believe that, I wouldn’t have offered her the job. And if she didn’t believe that I was equipped to lead this nation at such a difficult time, she would not have accepted. OK?”

For her part Mrs Clinton hinted at some of her anguish over a “very difficult” decision to leave the Senate and surrender her political independence to the man who vanquished her own presidential ambitions less than six months ago.

She said, however: “I thought of the daunting tasks ahead for our country: an economy that is reeling, a climate that is warming and, as we saw with the horrible events in Mumbai, threats that are relentless. The fate of our nation and the future of our children will be forged in the crucible of these global challenges.”

Mrs Clinton closed her remarks by saying: “Mr President-elect, I am proud to join you on what will be a difficult and exciting adventure in this new century.”

A close friend of the former First Lady said that both had “an immense incentive to make this relationship work”, adding that it was to Mr Obama’s credit that he had decided to have a strong secretary of state.

Bill Clinton, whose own tangled dealings abroad were once seen as a barrier to her being offered the job, described himself as a “deeply proud” husband.

Mrs Clinton had already earned the respect of foreign leaders and diplomats around the world, he said. “And Americans know that she will always put the security, values and the interests of our people first.”

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