Ten Democrats initially threw their hat into the ring to challenge George W Bush for the White House in the 2004 presidential election.
Former governor Howard Dean became the early front-runner and attracted the most political donations, after Al Gore, beaten narrowly in 2000, decided not to run.
But the late entrance of former Nato commander and four-star general Wesley Clark has made the contest for the Democratic nomination considerably more unpredictable.
Then the number of contenders was brought down to nine after Senator Bob Graham announced he was dropping out of the race on 6 October.
Click on a link below to read more about the key contenders.
Former Nato commander Wesley Clark announced his bid on 17 September, ending months of speculation.
The former general who led Nato forces during the Kosovo campaign has no political experience, but his military background could make him a formidable candidate anyway, some experts say.
The Kosovo campaign was successful, but many people will remember the celebrated dispute General Clark had with the British commander General Sir Mike Jackson.
For the first time since the Cold War, many Americans no longer feel safe in their homes and workplaces
He ordered General Jackson to stop Russian troops from taking Pristina airport as combat came to a close.
"I'm not going to start the Third World War for you," the British commander is reported to have replied.
With a distinguished record of service in Vietnam, Mr Clark opposed the US-led war in Iraq.
Analysts have speculated that the former general's decision to run will bring an even higher-profile candidate forward - Senator Hillary Clinton.
Howard Dean, a former physician and former governor of Vermont, has taken a striking early lead in the opinion polls.
With his medical background - including a degree from Yale - Mr Dean is said to be keen on health issues and also the environment. He is also a stark opponent of the war on Iraq.
In George Bush's America, the special interests own the government. In Howard Dean's America the government will again belong to the people
He started campaigning early, particularly in Iowa and New Hampshire which hold key primaries at the start of election season, and has stood out for his opposition to war in Iraq.
Until recently, he was unknown to many Democrats and the public at large. Now he is leading in opinion surveys in Iowa, which will hold a caucus on 19 January, and New Hampshire where
Democrats will hold a primary on 27 January.
He also leads in the fundraising stakes.
The Washington Post newspaper notes that history could be on his side, with a state governor winning all but one presidential election in the past quarter of a century.
North Carolina Senator John Edwards, a former lawyer, is considered one of the top Democrats in the US Senate.
Today, it's too hard for too many Americans to climb up the ladder of success...it is time for reforms that get us back to our democratic roots
He was also a short-listed contender for the vice-presidency under Mr Gore in the 2000 presidential election.
So far he has given little indication of his policies, other than promising to be a "champion" for the people, and is considered by Washington pundits to be a relative novice in the cut-throat world of US politics.
He is still regarded as a political novice, but his looks, youth and wealth could help his cause.
The great survivor in Democratic presidential politics, Richard Gephardt ran for the nomination as far back as 1988.
A Democrat Missouri congressman and former House minority leader in the US Congress, Mr Gephardt ran the party's house campaigns but resigned last year following its poor performance in the country's mid-term elections.
[Bush's] tax cuts targeted to those who need it the least... are shortsighted and misguided
He said he entered the race because he felt US President George W Bush was alienating key allies in the global community in the run-up to war with Iraq, but backed the war once hostilities began.
He has attempted to regain momentum and gain trade union support by proposing a major healthcare reform to cover the 41 million uninsured Americans.
Bob Graham (withdrawn)
Florida senator Bob Graham, a moderate Democrat, had been a late entry to the race and struggled to raise enough money to maintain his profile.
He delayed a formal announcement of his bid until May as he was recuperating from open-heart surgery and waiting for the Iraq war to subside.
As a two-term governor and three-term US senator from the state that tipped the presidency to George W Bush in 2000, he had legislative and executive experience to bring to the race.
grateful nation begins to see the return of its service members from Iraq, the Bush administration is moving to slash the veterans' healthcare system
Analysts had noted before his withdrawal that 66-year-old Graham needed to work harder to prove that he had the charisma and energy required to take on the president.
John Kerry, senator for the eastern US state of Massachusetts, formally declared his intention to run for the presidential nomination shortly before John Edwards.
I reject the radical vision of George Bush, a vision of government that suggests it's alright for the comfortable to be comforted at your expense
Mr Kerry is a decorated veteran of the Vietnam war, which may play well with the more conservative members of his party.
He is considered a liberal on social issues, which in turn will appeal to those on the left.
However detractors have expressed concern that his reserved personality may not fit with what the US public is seeking.
Congressman Dennis Kucinich, a former mayor of Cleveland, Ohio, entered the race on the basis of his opposition to the war in Iraq.
I am the only candidate who will take this country away from fear and war and tax giveaways, and use America's peace dividend for guaranteed health care for all
It is thought he will take votes from Howard Dean, because he sits on the same anti-war territory as Dean.
Kucinich is chairman of the congressional caucus and on the left of the Democratic party on every major issue, from healthcare to international development.
Senator Lieberman was Al Gore's running mate in the 2000 race. Mr Gore's decision not to stand freed Mr Lieberman from a promise not to run against his former partner.
Mr Lieberman was the first Jewish candidate for vice-president and now he hopes to be the first Jew to stand as a major party's choice for the White House.
President Bush - and some in my party - are flat wrong to close the door to sending more American troops now
His faith is important to him. He never campaigned on Saturdays - the Jewish Sabbath - in the 2000 race.
He is seen as perhaps the most conservative of the Democrats who have announced their candidacies so far.
Though he has experience and prominence from the national campaign with Mr Gore, he may face opposition from the more liberal sections of his party.
Carol Moseley Braun
Carol Moseley Braun, the first black woman elected to the US senate, declared in February 2002 that she would run for the White House, becoming the only woman in the field.
Chicago-born and educated, she was an early campaigner for a moratorium on the death penalty in her home state of Illinois. Executions were suspended there in 2000.
If you want practical solutions that solve multiple problems, turn the job over to a woman. Women deserve a chance to lead
After losing her senate seat in 1998, she was appointed ambassador to New Zealand, and returned to the US in 2001.
Commentators give her no chance of winning the nomination and her run is being seen as a way of derailing the campaign of Al Sharpton.
The Reverend Al Sharpton launched his bid for nomination with a vow to broaden the Democratic Party's appeal.
The civil rights leader says he is the only candidate with the credibility to reach out to disaffected black, Latino and young people.
I'm running on a platform of human rights and constitutional amendments that will greatly benefit all of the American people
Mr Sharpton, who describes himself as "anti-war, anti-death penalty, [and] anti-tax cut", has previously campaigned unsuccessfully to run for mayor of New York, and the Senate.
He is an outspoken critic on many issues, including police brutality, and the US military's controversial exercises on the Puerto Rican island of Vieques.
He is an avowed supporter of abortion rights.
Mr Sharpton has also criticised his fellow presidential nomination candidates, describing them as "rich white men" with little understanding of ordinary people.
His chances of nomination are extremely remote, most commentators say. However, some suggest that he might succeed in forcing issues onto the campaign agenda.
A recent Time magazine poll suggested Senator Hillary Clinton had more support among the party rank-and-file than any of her potential rivals.
There is continuing speculation as to whether she will run in 2004, despite her insistence that she will not.
I have said I am not running - if I knew another foreign language, I'd say it in that
Her run on the presidency had been expected in 2008, by which time she would have served a full term for New York state in the Senate.
But if President Bush is beaten by another Democrat this time, it would upset these calculations - challenging an incumbent president from inside the party would be extremely difficult.