DEMOCRATS: Barack Obama The only African-American in the US Senate, Obama (45) is the only potential Democratic candidate with the star power to rival Clinton.
His good looks, compelling personal story and brilliant oratory have made him a star within two years of becoming a senator. He opposed the Iraq war but was not in the Senate at the time of the vote to authorise the use of force. He announced this month that he is considering a presidential run in 2008 but his lack of legislative experience could count against him, as could racial prejudice.
John Edwards
A former senator and 2004 vice-presidential candidate, Edwards (53) has not announced his intention to run in 2008 but has made frequent visits to New Hampshire, Iowa and Wisconsin, which hold early primaries and caucuses. An energetic campaigner against poverty and inequality, he has travelled the US in recent weeks to support ballot initiatives to increase the minimum wage. He voted to authorise force in Iraq in 2002 but now says he regrets his vote. Edwards's failure to deliver his home state of North Carolina in 2004 has fuelled doubts about his appeal as a candidate in 2008.
John Kerry
Defeat in 2004 has not robbed Kerry (62) of his presidential ambitions, and he has been raising money energetically through his political action committee, Keeping America's Promise. Last month, he issued his strongest hint that he wants to run for the White House again, pointing out that Ronald Reagan and Richard Nixon had been defeated before they won the presidency. Democrats who blame Kerry for throwing victory away in 2004 may be less willing to give him a second chance.
REPUBLICANS
John McCain
Popular with Democrats and Independents, McCain (70) is mistrusted by some conservatives in his own party but remains the Republican front-runner for 2008. A fiscal and social conservative and a foreign policy hawk, McCain is nonetheless willing to break ranks with Republicans, opposing harsh interrogation methods for suspected terrorists and advocating immigration reform to allow many illegal immigrants to remain in the US and apply for citizenship. His age and quick temper could be liabilities in a presidential campaign.
Mitt Romney
As a Republican governor of liberal Massachusetts, Romney (59) this year signed legislation that gives healthcare to almost all the state's citizens without increasing taxes. A social conservative who has strongly opposed partnership rights for gays and lesbians, Romney ought to appeal to evangelical Christians. His biggest problem may be that he is a Mormon.
Rudy Giuliani
As New York's mayor on September 11th, 2001, Giuliani (62) became a national hero who could, as a Republican presidential candidate, reach out to Democratic voters. Tough on national security and crime, Giuliani is liberal on social issues, including abortion and gay rights. Although this places him in the mainstream of US opinion, his liberalism could deny him the nomination.