US Democratic presidential candidates Bernie Sanders and Hillary Clinton moved past the latest tempest over a breach of campaign's voter data, shifting Saturday night's debate into a fierce yet civil discussion of the economy, national security and the federal role in legislating gun control.

The candidates also took turns hitting out at Donald Trump, hurling outrage about the Republican presidential candidate's fear-mongering and recent controversial comments about immigrants - in particular, his call for a ban on Muslims entering the United States.

"Mr. Trump has a great capacity to use bluster and bigotry to inflame people," Clinton said.

Candidates differ over military engagement in Middle East

Discussing the Middle East, there was broad agreement that the United States should not launch a ground war to defeat the so-called "Islamic State." But the candidates differed in the tactics they would take and whether the nation should seek regime change in Syria.

Clinton called for a no-fly zone over part of Syria and insisting that the US must seek to remove Syrian President Bashar al-Assad from power.

"If the United States does not lead, there is not another leader - there is a vacuum," she said.

Sanders - who opposed the 2003 Iraq invasion - disagreed, saying the US should first seek to defeat IS but show caution over toppling governments.

"Secretary Clinton is too much into regime change and a little bit too aggressive without knowing what the unintended consequences might be," Sanders said. "Yes, we could get rid of Assad tomorrow, but that would create another political vacuum that would benefit ISIS."

And O'Malley, who is currently running a distant third in polls, pointedly noted how past US-led regime changes bred chaos. He singled out Libya in 2011, when Clinton was the top US diplomat and supported ousting Moammar Gadhafi, only to see the country become a safe haven for jihadist militants.

"We probably let our lust for regime toppling get ahead of the practical considerations for stability in that region," O'Malley said.

On economic inequality

Sanders, who has made addressing income inequality the cornerstone of his campaign, pledged to invest in free access to higher education and health care while also reigning in the political influence of the financial industry.

Sanders said chief executives of large multinational corporations "ain't going to like me, and Wall Street is going to like me even less."

Clinton said she thinks "everybody should" love her, including corporate America. She has faced criticism for her close ties to Wall Street and for the money she's raised from the financial services industry.

Clinton also questioned the affordability of some of Sanders' proposals such as creation of a single-payer health care system and tuition-free college, suggesting these plans would lead to higher taxes on working families.

"I don't think we should be imposing big new programs that are going to raise middle-class families' taxes," Clinton said. "We've got to get back to where people can save money again, where they can invest in their families."

Instead, she said she would focus on lowering taxes for the lower income brackets. She said as president she wouldn't raise taxes on families making $250,000 (230,000 euros) or less per year.

O'Malley throws down the gauntlet on gun control

Some of the sharpest exchanges were at the onset when O'Malley accused his rivals of being soft on gun control. He said both Clinton and Sanders had adopted more aggressive positions on gun control only after this year's increase in mass shootings.

Sanders said he had lost an election in Vermont for a gun-control stance and Clinton said she had backed gun-control measures.

Just over six weeks remain before the first votes are cast in the nomination race on February 1 in Iowa, and Sanders and O'Malley are running out of time to blunt the momentum of the former secretary of state, who is 25 points ahead of rival Sanders in national polling compiled by RealClearPolitics.com.

The debate, the third for Democrats, had low viewership given that it was scheduled on the last weekend before Christmas, when many Americans have turned their attention to the holidays.

Both the Sanders and O'Malley campaigns have complained the Democratic Party leadership scheduled the debates on nights with low TV viewership in order to favor Hillary Clinton, who is better known than her challengers.

jar/sms (AP, Reuters, AFP)