US Democrats will seek to unite the party for its convention to nominate presidential candidate Barack Obama as Republicans stirred up a rift with disaffected supporters of his former rival Hillary Clinton.
Mr Obama faces a challenge this week to try to heal the party rift, draw a sharp contrast between himself and Republican rival John McCain and back up his soaring oratory with specifics of what he would do if he wins the White House.
As they prepared Thursday's acceptance speech, Democrats gathering for the convention in Denver have seen polls showing backing from Ms Clinton supporters, who lost the contest for the party's presidential nomination, slipping even as the race between Mr Obama and Mr McCain tightened.
Mr Obama spokesman Robert Gibbs told CNN the choice before voters in November would be between Mr Obama and Mr McCain, and noted that Ms Clinton herself had publicly thrown her support behind the Illinois senator.
"If we put the choice in front of delegates here and voters all across this country, who's going to help rebuild this economy and put your family back to work, who's going keep your family safe at night, who's going to reduce our dependence on foreign oil ... The best person to do those things isn't John McCain, it's Barack Obama," Mr Gibbs said.
"Hillary Clinton's worked with both of these guys and she's come to the same conclusion. Barack Obama is her guy," he said.
But senior McCain aide Carly Fiorina said disgruntled women supporters of Hillary Clinton "want a leader whose judgment and experience they can trust."
Ms Fiorina also threw oil on the flames of the Democrats' split, saying many Democratic women were "stunned" that Obama praised his vice-presidential pick Senator Joe Biden as a good debater and campaigner "when Hillary Clinton was clearly in the
Democratic primaries the woman who, the person, who gathered the most votes - 18 million of them - was a great debater and a great campaigner."
Some Clinton supporters had still wanted Mr Obama to pick her as his running mate.
Many delegates in Denver were looking to see to what extent Ms Clinton, and her husband, former President Bill Clinton, will actively rally her supporters behind Obama in speeches to the convention this week.
As Mr Obama (47) enters the convention he has yet to answer doubts among many Americans about where he would take the country if elected but most Democrats are confident the man who would be America's first black president is in a strong position to defeat Vietnam war hero Mr McCain (71).
Mr Obama's spokesman, Bill Burton, laid out two goals for the convention.
"We want to make sure people know exactly who Senator Obama is and where he wants to take the country, and two, that voters know their choice in this election, between Barack Obama, who wants to fundamentally change the way business is done in Washington, and John McCain, who is just more of the same of what we have had over the course of the last eight years," he said.
Mr Obama "needs to change the direction of his campaign" by tying Mr McCain more closely to President George W. Bush, unpopular due to the Iraq war and weak economy, said Democratic strategist Doug Schoen, who worked in the Clinton White House.
Mr Obama also needs to limit the uplifting rhetoric and outline sharper differences with Mr McCain on tax policy, energy, housing and job creation, Schoen said.
"He's got to be focused, simple and clear, rather than elegiac. This is not a great novel. This is a short, clear, focused discussion ... Unless it is clear and real simple, he has failed."
The opening night on Monday at the convention is dedicated to highlighting Mr Obama's life story, his commitment to change, and those calling for a new direction in the country.
The keynote speaker will be Mr Obama's wife, Michelle.
The son of a black father from Kenya and a white mother from Kansas, Mr Obama spent formative years in Hawaii and Indonesia, worked his way through college and began his political career as a community organizer in Chicago.
Tonight will also feature a tribute to Massachusetts Senator Edward Kennedy, a Democratic Party icon now battling brain cancer. A Kennedy family confidant told the Boston Globenewspaper Mr Kennedy would attend the convention.
"He is definitely planning to be here," he said. "The whole Kennedy family will be in a special section.