Donald Trump and Hillary Clinton are in clear control of the races to be the presidential nominees of their parties, the latest national polls show just days before the first votes are cast in Iowa next Monday.
Mr Trump’s support stands at 41 per cent, according to the latest CNN/ORC poll. More than two-thirds of Republicans said in the survey that they expect him to win the party’s nomination.
His nearest rival, Texas senator Ted Cruz, has 19 per cent support. No other Republican candidate reached double-digit figures in the poll.
Florida senator Marco Rubio, who has emerged as the favourite of the party's more moderate establishment wing, polled at 8 per cent nationally, followed by retired neurosurgeon Ben Carson at 6 per cent and former Florida governor Jeb Bush at 5 per cent.
The figures remain largely unchanged since the same poll was carried out in December.
Two-horse race
In the more closely watched race in Iowa, a new tracking poll released by Connecticut-based
Quinnipiac University
showed that the first nominating contest has become a two-horse race between Mr Trump and Mr Cruz.
In addition, Mr Rubio’s place as a distant third has declined by two points in as many weeks.
The poll put the two Republican front-runners in a dead heat in the Iowa caucus. Mr Trump’s lead of 31 per cent against Mr Cruz’s 29 per cent fell within the margin of error.
A weekly tracking poll by NBC News and Survey Monkey, put Mr Trump’s lead at 39 per cent among Republicans 20 points ahead of Mr Cruz.
The same poll put Mrs Clinton's lead at 51 per cent, 14 points ahead of closest rival, self-described democratic socialist Bernie Sanders.
Making final pitches to Iowans before the state’s caucuses, Mrs Clinton and Mr Sanders made passionate pleas to voters in a town hall in Des Moines on Monday.
Unusually confrontational
Adopting sharply different approaches in a format that is softer than the head-to-head debates, Mr Sanders was unusually confrontational, objecting to his rival’s attacks and challenging her record.
Rejecting Mrs Clinton’s charges that he is not prepared to be commander-in- chief, Mr Sanders aimed to show he was more closely aligned with the Democratic base and to contrast his positions with Mrs Clinton’s on issues on which she has pivoted.
"I voted against the war in Iraq. Hillary Clinton voted for the war in Iraq," an animated Mr Sanders said. "I led the effort against Wall Street deregulation. See where Hillary Clinton was on the issue."
Mrs Clinton attempted to deflect criticism of being a newcomer to the economic inequality debate that Mr Sanders used first to fire up grassroots liberals, making the Iowa caucus a far closer race.
One of her liveliest contributions came in response to a question from a young man who asked why millennials think her dishonest and why they aren’t as enthusiastic about her campaign as Sanders’s. Mrs Clinton blamed the attacks she has endured throughout her career.
“People have thrown all kinds of things at me,” she said. “You have to say to yourself, why are they throwing all of that? Well, I’ll tell you why: because I’ve been on the front lines of change and progress since I was your age.”
Her strong defensive posture came as her campaign released an ad showing videos dating back more than 40 years to her early time in public life advocating for women’s and children’s issues.
