Barack Obama may have won the Democratic presidential nomination with his dream of uniting America, but yesterday he faced a more immediate task: to heal the red raw wounds in his own party.

The victory he achieved in his epic 16-month fight with Hillary Clinton marked a significant milestone for the US – or, indeed, for any Western democracy – showing that a country scarred by racism had progressed far enough to back a black man standing for its highest office.

“Tonight we mark the end of one historic journey with the beginning of another – a journey that will bring a new and better day to America,” he said at a mass rally in front of 17,000 people in St Paul, Minnesota, on Tuesday night. ”

He made a point of thanking his white grandmother, who he has suggested previously harbours her own racist attitudes, for helping to “make me the man I am”.

The historic nature of Mr Obama’s win was noted yesterday by the White House and by Condoleezza Rice, the Secretary of State, who said it showed “the United States is an extraordinary country”.

But Mr Obama knows that the Democratic primary season, the closest in memory, has also revealed deep divisions, not just on race, but also on gender, class and age, which could yet deny him the presidency.

Mrs Clinton, who by some counts beat Mr Obama in the popular vote, consistently won more support among whites, Hispanics, the working class, women and the elderly.

Tuesday night’s final two primaries delivered a split decision that reflected how close the nomination battle had been over the previous 52 contests: South Dakota voted for Mrs Clinton while Montana backed Mr Obama. By the time the results rolled in, the race was already over with Democratic super-delegates finally tipping the balance decisively towards Mr Obama. But she refused to concede.

There are many injured feelings and battered egos in her camp. Bill Clinton has talked of a conspiracy by people to cover up polls showing she is best placed to win a general election. Others complain of sexism, media bias and the arrogance of the Obama campaign.

It was not until after midnight that Mr Obama spoke to Mrs Clinton by telephone, when she eventually called him back, having apparently been too busy to return two earlier messages. Yesterday, after delivering a speech to the pro-Israel Aipac conference in Washington, he told reporters that he had spoken to her again “and we’re going to be having a conversation in the coming weeks”. He added: “I’m very confident that we’re going to have a united Democratic party at the general election in November.”

The Democratic leadership, including Harry Reid, the Senate majority leader, Nancy Pelosi, the House of Representatives Speaker, Howard Dean, the party chairman, and Joe Manchin, head of the Governors Association, delivered a blunt message yesterday that they want unity sooner, not later. “The voters have spoken,” they said in a joint letter. “Democrats must now turn our full attention to the general election. To that end, we are urging all remaining uncommitted super-delegates to make their decisions known by Friday of this week so that our party can stand united and begin our march toward reversing the eight years of failed Bush/ McCain policies that have weakened our country.”

For the moment, however, Mr Obama must continue treating Mrs Clinton with kid gloves. He routinely lavishes praise on her as one who has opened up opportunities for all women, including his two daughters. Senator Dick Durbin, one of his leading backers, yesterday described the “awkward situation” that existed as they waited or her to concede, adding: “I don’t want to push her, nobody wants to push her.”

Mr Obama’s aides say privately that he has little or no desire to see her as vice-president. They are alarmed at the prospect of having her and her husband in the White House as a focal point for dissent and “Clintonian machinations”. Nor have they forgiven her for attacks on Mr Obama’s experience, judgment and character over the past few months.

His camp believes the party will inevitably begin to coalesce in the coming weeks, pointing out that there are many other senior Democratic politicians who could broaden his appeal in regions such as the Appalachians without having to have Mrs Clinton tainting his ticket. Even some of her closest supporters voiced doubts yesterday about whether such a partnership would work.

Ed Rendell, the Governor of Pennsylvania, said: “Generally a lot of politicians don’t like to put somebody like that on the ticket. You know rule one for the vice-president is make sure you never upstage the president, right? Hillary Clinton in some ways couldn’t help but upstage, even if she was trying not to.”

But Mr Obama has also made plain there is a tough general election battle looming and that he needs Mrs Clinton on board rather than standing, embittered, on the wayside.

John McCain’s strategists have already decided to paint Mr Obama as naive, inexperienced and weak. The Republican nominee-in-waiting is even making his own bid for the mantle of change – a word he uttered no fewer than 30 times in a speech on Tuesday night. “The wrong change looks not to the future but to the past for solutions that have failed us before and will surely fail us again,” he said. “I have a few years on my opponent, so I am surprised that a young man has bought into so many failed ideas.”

Mr Obama replied swiftly: “There are many words to describe John McCain’s attempt to pass off his embrace of George Bush’s policies as bi-partisan and new. But change is not one of them.”

The winning team

Michelle Obama, wife
Sharp-witted lawyer who has often reminded audiences that her husband is a mere mortal. A formidable figure, she has done much to authenticate Obama’s credentials among blacks, but must beware of repeating lines such as “for the first time in my adult life, I am proud of my country”

David Axelrod, chief strategist
Former political journalist turned consultant, who laces his idealism with a heavy measure of the Chicago street. Despite close ties to Hillary Clinton and John Edwards, he decided that to get Obama – a friend since 1992 – elected president would “mean I had accomplished something great in my life”

David Plouffe, campaign manager
Quietly spoken long-time Democratic operative who has maintained strict discipline in a relatively leak-free team. Crafted the strategy of getting lift-off in Iowa and then focusing on smaller states where huge wins cancelled out Clinton’s big state advantages

Susan Rice, foreign policy adviser
One of several former members of the Clinton Administration to jump ship. She has fleshed out the bones of Obama’s policy of engaging with America’s enemies. May well be the second black woman called Rice to be appointed national security adviser by a new president

Robert Gibbs, communications chief
Ever-present at Obama’s side since quitting the John Kerry campaign in 2003. He plays basketball with Obama and cooks for him, talks about how much they miss their children on the campaign trail

Reggie Love, body guy
The former Duke University basketball player is Obama’s workout partner, friend and the “little brother he never had”

Times Recommends

• Both sides blame US for worsening relations
• Stieg Larsson: losing the plot over his cash
• Odd creature paralysed by incompatible parts