US:With almost 20 candidates clamouring for attention a year before the first primary votes, each party has three frontrunners. On the Democratic side, New York senator Hillary Rodham Clinton is the favourite but faces serious challengers in Illinois senator Barack Obama and former vice-presidential candidate John Edwards.
The Republican smart money is on Arizona senator John McCain, whose strongest rivals are former New York mayor Rudy Giuliani and former Massachusetts governor Mitt Romney.
Other Democrats who have taken the first legal step towards running are Connecticut senator Chris Dodd, New Mexico governor Bill Richardson, former Iowa governor Tom Vilsack, Ohio congressman Dennis Kucinich and former Alaska senator Mike Gravel.
The other Republicans in the race are Kansas senator Sam Brownback, former Wisconsin governor Tommy Thompson, California congressman Duncan Hunter, Texas congressman Ron Paul, Colorado congressman Tom Tancredo and former Virginia governor Jim Gilmore.