The first one-to-one Democratic debate saw Hillary Clinton and Bernie Sanders clashing over Wall Street and foreign policy.
Hillary Clinton cast Bernie Sanders as an idealist who will not get things done and Sanders accused the former Secretary of State of being too tied to the establishment to achieve real change.
The MSNBC debate in New Hampshire was their first since the Democratic race was whittled down to two this week.
Without a third person on stage, the policy differences were laid bare.
Hillary Clinton said Bernie Sanders’ proposals such as universal healthcare were too costly and unachievable.
She went after her rival aggressively over his attempts to portray her as being in the pocket of Wall Street because of the campaign donations and the fees she had received for after-dinner speeches.
Vermont Senator Bernie Sanders used a favorite attack line against Hillary Clinton that she backed the Iraq War, but she questioned his foreign policy expertise.
The debate comes five days before the second state-by-state contest in the battle for the presidential nominee, in New Hampshire on February 9.
Despite the tensions over policies, the debate ended on a warm note, when Hillary Clinton said the first person she would call would be Bernie Sanders, if she won the nomination.
The debate was their first without the presence of the former governor of Maryland, Martin O’Malley, who quit the race on February 1.
Martin O’Malley was a distant third in the first state to vote, Iowa, where Hillary Clinton narrowly beat Bernie Sanders after a prolonged count.
Bernie Sanders holds a big lead in polls in New Hampshire, which borders the state where he is a senator, Vermont.
Both Republican and Democratic parties will formally name their presidential candidates at conventions in July.
Americans will finally go to the polls to choose the new occupant of the White House in November.
VIDEO Donald Trump has mocked former secretary of state Hillary Clinton for apparently taking a toilet break during a televised Democratic debate.
The Republican presidential hopeful told supporters at a rally in Michigan:
“I know where she went. It’s disgusting.”
Hillary Clinton returned to the stage late after an advert break during December 19 debate with her party rivals for the presidential nomination.
Donald Trump also said Hillary Clinton had been “schlonged” by Barack Obama in 2008.
Using a vulgar Yiddish term, the Republican frontrunner was referring to Hillary Clinton’s defeat to the then senator in the primary contests that year.
Photo CBS News
“Even her race to Obama. She was going to beat Obama. I don’t know who’d be worse. I don’t know. How does it get worse? “She was favored to win and she got schlonged, she lost.”
It is not the first time Donald Trump has referred to women in a controversial way.
In August, the property tycoon implied that he received tough questions from Fox News debate host Megyn Kelly because she was menstruating.
He has previously described comedian Rosie O’Donnell as a “fat pig”.
Hillary Clinton and Donald Trump have been feuding in recent days over claims she made that ISIS was using Donald Trump’s videos as a recruiting tool.
The billionaire has called for Muslims to be banned from entering the United States, in light of the San Bernardino deadly terror attack carried out by a radicalized Muslim couple.
Donald Trump, who has no political experience, leads the polls nationally among Republican voters, and is also ahead in some key states.
The primary contests begin at the start of February and the presidential election is in November 2016.
VIDEO Democrat presidential hopeful Bernie Sanders has apologized to fellow candidate Hillary Clinton after his staff stole valuable voting data from her campaign. “This is not the type of campaign that we run,” Bernie Sanders said during Abc New debate on December 19.
The candidates criticized Republican frontrunner Donald Trump for his call to ban Muslims from entering the United States.
They clashed over Syria, with Bernie Sanders accusing Hillary Clinton of being set on regime change while she said US leadership was needed.
Former Maryland Governor Martin O’Malley also took part in the debate in Manchester, New Hampshire.
Former secretary of state Hillary Clinton remains the frontrunner.
On Syria, Hillary Clinton insisted that the US should seek to remove President Bashar al-Assad from power.
“If the US does not lead, there is not another leader – there is a vacuum,” she said.
Bernie Saunders however argued that the US should first concentrate on defeating ISIS.
“Getting rid of dictators is easy, but you have to think about what happens the day after,” he said.
Both the main speakers had strong words for Donald Trump, with Hillary Clinton calling him “the biggest recruiter for ISIS” and saying he used “bigotry and bluster to inflame people”.
The debate was the first for Democrats since 14 people were killed by a married couple that the authorities say had been radicalized.
All three candidates said it was important to work more closely with Muslim-American communities to tackle radicalism at home.
Bernie Sanders admitted that on two occasions his campaign could see proprietary data from Hillary Clinton’s campaign following computer breaches – which he said were the fault of the software vendor.
He said that the most recent breech involved inappropriate behavior by one of his staff members, adding that person had now been dismissed.
Bernie Sanders said that the Democratic Party’s decision to temporarily suspend his campaign’s access to the strategically crucial database was “an egregious act”.
The Sanders campaign on December 18 filed a lawsuit against the Democratic National Committee in a federal court to restore its access to the voter data.
Strategically important information on voters is contained in the database, which campaigns use to decide strategy.
That data takes on a crucial role as campaigns prepare for early primary voting in just over a month’s time.