Republicans and Democrats scrambling for their party's 2016 nomination for president descended on the tiny New England state of New Hampshire on Tuesday, leaving behind the Iowa caucuses where Ted Cruz, a fiery, conservative Texas senator loathed by his own party's leaders, swept to victory over billionaire Donald Trump and Florida Senator Marco Rubio.
Among Democrats, Bernie Sanders rode a wave of voter enthusiasm to a virtual tie with Hillary Clinton, long considered her party's front-runner.
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However, the former secretary of state, senator from New York and first lady edged past the Vermont senator in a race the Iowa Democratic Party called the closest in its caucus history.
The Iowa Democratic Party said Tuesday that it would not do any recount of the close results, and a spokesman for the Sanders campaign said it does not intend to challenge the results of the caucuses.
The outcome in the country's first nominating contest drew a line under voter dissatisfaction, especially among Republicans, with the way government in Washington operates, with anger over growing income inequality and fears of global turmoil and terrorism.
Cruz's victory in Monday's caucuses, which drew a record turnout, was a blow to Trump, the real estate mogul who has roiled the Republican field for months with controversial statements about women and minorities.
Trump holds lead in polls
Cruz now heads to next Tuesday's first-in-the nation primary vote in New Hampshire as an undisputed favourite of the furthest right voters, including evangelical voters and others who prioritize an abrupt break with President Barack Obama's policies.
But Trump still holds a commanding lead in New Hampshire and national polls.
New Hampshire has historically favoured more moderate candidates than Iowa, and more than 40 per cent of the state's electorate are not registered in any political party, giving them the power to choose which party's primary to vote in on Feb. 9.
Cruz on Tuesday suggested he was focused on New Hampshire but also on South Carolina, which votes 11 days later.
Trump came in second slightly ahead of Rubio, whose stronger-than-expected finish could help cement his status as the favourite of mainstream Republican voters who worry that Cruz and Trump are too caustic to win the November general election.
Trump sounded humble in defeat, saying he was "honoured" by the support of Iowans. And he vowed to keep up his fight, telling cheering supporters that "we will go on to easily beat Hillary or Bernie or whoever the hell they throw up."
Sanders faces uphill battle
In the Democratic race, Iowa caucus-goers were choosing between Clinton's pledge to use her wealth of experience in government to bring about steady progress on party ideals and Sanders' call for radical change in a system rigged against ordinary Americans. Young voters overwhelmingly backed Sanders.
Clinton was hoping to banish the possibility of dual losses in Iowa and in New Hampshire, where she trails Sanders, who is from neighbouring Vermont.
Sanders had hoped to replicate Obama's pathway to the presidency by using a victory in Iowa to catapult his passion and ideals of "democratic socialism" deep into the primaries.
Sanders still faces an uphill battle against Clinton, who has deep ties throughout the party's establishment and a strong following among a more diverse electorate that plays a larger role in primary contests in February and March.
Huckabee, O'Malley bow out
Iowa has long led off the state-by-state contests to choose delegates for the parties' national conventions. Historically, a victory has hardly assured the nomination, but a win or an unexpectedly strong showing can give a candidate momentum, while a poor showing can end a candidacy.
Some of the establishment Republican candidates have been focusing more on New Hampshire than Iowa, including former Florida governor Jeb Bush, Ohio Governor John Kasich and New Jersey Governor Chris Christie.
The caucuses marked the end of at least two candidates' White House hopes. Former Maryland governor Martin O'Malley ended his longshot bid for the Democratic nomination, and former Arkansas governor Mike Huckabee dropped out of the Republican race.
The state's 30 Republican delegates to the national convention are awarded proportionally based on the vote, with at least eight delegates going to Cruz, seven to Trump and six to Rubio.
Clinton's victory in Iowa means she will collect 23 delegates and Sanders will win 21. With her advantage in superdelegates — the party officials who can support the candidate of their choice — Clinton now has a total of 385 delegates. Sanders has 29.