Republicans set for first hurdle
Republican presidential candidates have one week to convince voters in Iowa that they are the one to defeat President Barack Obama next year.
The state holds the country's first nominating contest on January 3 - state-wide precinct caucus meetings. They will probably reduce the seven-person field and shape the coming six-month string of state-by-state primary elections and caucuses leading up to the Republican National Convention that officially names a candidate in August.
Mr Obama is vulnerable because of national dissatisfaction with the economy that has been extremely slow to pull out of the Great Recession. But the tangle of Republicans vying for the nomination to challenge the president in November - and fundamental splits over ideology - have left the party divided.
Republican Party chairman Reince Priebus discounts the chaotic situation, saying the campaign is still in its early stage and calling it "a horse race".
National front-runner Mitt Romney, the former Massachusetts governor, is disliked and not trusted by conservative Republicans who have thrown their support behind a series of other candidates whose policy promises are more palatable to them. But each of those candidates, Michele Bachmann, Rick Perry, former businessman Herman Cain and now former House of Representatives Speaker Newt Gingrich have all grabbed support and quickly risen in the polls before losing steam under closer scrutiny by voters and the news media.
Many of those expected to take part in the Iowa caucuses remain undecided. And while Mr Romney appears stronger in the state than he had earlier, polls show his biggest rivals are Mr Gingrich and the libertarian-leaning Ron Paul.
Mr Romney, who finished second in the 2008 Iowa caucuses in his first run for the presidency, released a new television commercial for the state in which he touted his background as a conservative businessman and cited a "moral imperative for America to stop spending more money than we take in. It's killing jobs."
He returns to Iowa after a quick stop in his long-established stronghold of New Hampshire, which holds its the nation's first primary on January 10, exactly one week after the Iowa caucuses.
Mr Romney has a well-funded and well-organised campaign nationally and in Iowa, as well as allies who are spending heavily on television advertisements through an independent organisation known as a super PAC, or super Political Action Committee.
He has recently invested more time and resources in Iowa, hoping to eke out a victory in the caucuses at a time when the party's social conservatives have yet to coalesce behind a single candidate.