Republican hopefuls for the US presidency have held their last debate before the nominating elections begin with the Iowa caucus on 3 January.
The race is heating up for both Republicans and Democrats
Opinion polls suggest the battle for Iowa and the momentum it can give a candidate's campaign is between Mitt Romney and Mike Huckabee.
The Democratic contenders hold their last debate in Iowa later in the day.
Hillary Clinton, who leads national polls, has seen some surveys give Barack Obama the edge in Iowa.
Polls also suggest the two Democrats are virtually tied in New Hampshire, which holds its primary on 8 January.
CURRENT KEY DATES
3 Jan: Iowa caucus
8 Jan: New Hampshire primary
19 Jan: South Carolina primary (Rep)
29 Jan: Florida primary; South Carolina primary (Dem)
5 Feb: some 20 states including California, New York, New Jersey
Candidates who do not do well in early elections tend to drop out, so giving the states which decide first a greater say in the electoral process which will culminate in the presidential election on 4 November 2008.
The Republicans' Iowa debate on Wednesday saw candidates largely refrain from attacking one another, opting instead to reiterate their position on a host of issues from trade to taxes.
Away from the debate, however, the race has taken on a more aggressive tone, especially between Mr Romney and Mr Huckabee, who according to opinion polls now leads the race for Iowa.
Mr Romney's campaign this week began running a negative TV commercial accusing Mr Huckabee of being soft on illegal immigration.
Mr Huckabee, a Southern Baptist minister, has for his part become involved in a new row over Mr Romney's Mormon faith.
Interviewed by the New York Times magazine, Mr Huckabee said he believed Mormonism was a religion. He was then quoted as saying: "Don't Mormons believe that Jesus and the devil are brothers?"
His campaign later said the remarks had been taken out of context and Mr Huckabee said he had apologised to Mr Romney after the Iowa debate.
Mr Romney, speaking on Fox News, said he had accepted the apology for what he called a "traditional smear" on the Mormon faith.
"We really shouldn't be attacking a person's religion in this nation," he said.
Former New York Mayor Rudy Giuliani continues to lead in national polls and has not campaigned heavily in Iowa, judging he is unlikely to win over social conservatives who dominate the Republican electorate there.
Hillary Clinton has been the Democratic front-runner for months
The Democratic candidates are set to gather in Iowa for a debate beginning at 1900GMT on Thursday.
Their race has also begun to heat up with opinion polls suggesting fluctuating fortunes.
Sen Clinton has seen her closest rival, Sen Obama, move slightly ahead according to some polls for Iowa and New Hampshire.
Correspondents say third-placed Democrat John Edwards will be hoping the two front-runners cancel one another out.