Barack Obama took the first big step to winning the Democratic nomination on Thursday with a victory in Iowa, while underdog Mike Huckabee capped a stunning political rise to beat Republican rival Mitt Romney.
Obama, an Illinois senator bidding to make US history as the first black president, won the first Democratic test on the road to the White House with a comeback triumph over New York Sen. Hillary Clinton and former North Carolina Sen. John Edwards, who were in a tight battle for second.
Huckabee, a former Arkansas governor and ordained Baptist minister, beat Romney fairly easily despite being dramatically outspent by the wealthy former Massachusetts governor and venture capitalist.
Both Obama and Huckabee once trailed their better-known rivals Clinton and Romney in their race to be on the November election ballot, but rode a wave of grass-roots enthusiasm to victories in the most hotly contested presidential campaign in Iowa history.
The 2008 campaign is the most open presidential race in more than 50 years, with no sitting president or vice president seeking his or her party's nomination.
For the winner in Iowa, the prize is valuable momentum and at least a temporary claim to the front-runner's slot in their battle to win the party's presidential nomination in the November election.
All eyes now turn to New Hampshire, which holds the next contest on Tuesday and where Romney and Clinton will face high-pressure bids to revive their candidacies.
The loss was a heavy blow to Clinton, the former first lady who a few months ago was considered in some quarters the almost certain Democratic nominee. She now faces immense pressure to turn around her campaign in New Hampshire over the next five days.
Edwards, who at one time led polls in Iowa and finished a strong second here during a failed 2004 presidential bid, also will face questions about the viability of his candidacy as he goes forward.
Obama's win effectively makes him the candidate to beat among Democrats, and a win next week in New Hampshire could put him in prime position to capture the nomination. The next big contest would be in South Carolina, where more than half of the voters in the Democratic primary are likely to be black.
Iowa kicks off race
Iowa voters filled gathering spots in more than 1,700 precincts around the state to declare a presidential preference in Iowa's caucuses, which open the state-by-state battle to choose candidates in the November 4 election to succeed President George W Bush.
In the Democratic caucuses, voters debated their options and cajoled their neighbors to switch to their candidate. Republicans conducted essentially a preference poll, casting votes soon after the caucus begins.
For Republicans, Huckabee's upset reshaped a race where no candidate has been able to claim front-runner status.
Iowa, where a sizable bloc of religious conservatives had fueled Huckabee's rapid rise, represented perhaps the best chance for the former Arkansas governor to break through with a win.
He will face tougher going in New Hampshire, where there are fewer evangelicals, and he has lingered well behind Romney and Arizona Sen. John McCain in polls.
Romney, a former governor of Massachusetts who has faced questions about his Mormon faith during the campaign, launched aggressive advertising campaigns against Huckabee and McCain in recent weeks.
Iowa's opening contest in the nominating battle has traditionally served to winnow the presidential field of laggards and elevate some surprise contenders.
The Democrats, who said more than 210,000 turned out to surpass the 124,000 Iowans who participated in 2004, reported record turnout. Republicans could challenge their record of 87,000 caucus participants in 2000.