The Paris attacks pushed the Islamic State to the top of the agenda at the second US Democratic presidential debate as the candidates clashed on what caused the rise of the militant group and how to deal with it.
The night will be most remembered for a rare gaffe by the Democratic frontrunner, Hillary Clinton, who invoked other terror attacks, those of September 11th, 2001 on New York, to defend her receipt of campaign contributions from big Wall Street donors.
The CBS-hosted debate, held in the first nominating state of Iowa, began with a moment's silence to the victims in Paris.
The televised debate was a tame affair with respectful disagreements, as Vermont senator Bernie Sanders aimed to close Ms Clinton's big lead and former Maryland governor Martin O'Malley sought a breakthrough moment to transform his long-shot campaign.
On the most pressing issue of the night, Ms Clinton, Barack Obama’s first secretary of state, echoed the president’s strategy to defeat the IS terror group, saying that the militants could only be defeated by a US-led coalition.
“This cannot be an American fight, although American leadership is essential,” she said.
Mr O’Malley, who lags her by 52 points in the polls, disagreed with her, though the difference in his views were largely semantic.
“This actually is America’s fight. It cannot solely be America’s fight,” he said.
Mr Sanders pledged as president to “rid our planet of this barbarous organisation called ISIS” without saying how he would do it.
Appearing to distance herself from Mr Obama, who remarked a day before the attacks that IS had been “contained,” Ms Clinton said that the group “cannot be contained; it must be defeated.”
Defending the White House’s much-criticised response, Ms Clinton said the US could not take most of the blame for the rise of IS.
"I don't think the United States has the bulk of the responsibility," she said.
Bernie Sanders, the socialist senator for Vermont who is 21 points behind Ms Clinton in the polls, objected.
"I don't think any sensible person would disagree that the invasion of Iraq led to massive instability that we are seeing right now," he said.
He went further landing a blow on Ms Clinton by tying her vote as a senator for the 2003 invasion to the growth of the militant groups.
“I would argue that the disastrous invasion of Iraq, something that I strongly opposed has unravelled the region completely and led to the rise of al-Qaeda and to ISIS,” he said.
On an issue that later fuelled attacks by Republicans, Ms Clinton refused to say the United States was at war with “radical Islam,” preferring to say that the war was against “jihadists.”
The biggest hit of the night on Ms Clinton was, however, self-inflicted when she referred to the 9/11 terror attacks in her defence of an attack from Mr Sanders about her ties to Wall Street.
Asked what he thought of her plans for the big banks, Mr Sanders said: “Not good enough!” He went on to question whether she could challenge Wall Street when she had received so much money from it.
“Why over her political career has Wall Street been a major, the major campaign contributor to Hillary Clinton?” he asked. Big donors “expect to get something,” he said. “Everybody knows that.”
Ms Clinton accused him of impugning her integrity.
When Sanders disputed this, saying: “No, I have not,” Ms Clinton interjected, “Oh, wait a minute Senator,” to intakes of breathe from the audience during the most heated exchange of the two-hour debate.
“I represented New York and I represented New York on 9/11 when we were attacked. Where we attacked? We were attacked in downtown Manhattan where Wall Street is,” she said.
“I did spend a whole lot of time and effort helping them rebuild. That was good for New York. It was good for the economy, and it was a way to rebuke the terrorists who had attacked our country.”
A debate moderator later put to Ms Clinton a message posted on social media website Twitter in which a Iowa law professor criticised her for invoking 9/11 to defend her Wall Street connections.
“I’m sorry that whoever tweeted that had that impression,” she said. “Because I worked closely with New Yorkers after 9/11 for my entire first term to rebuild, and so yes, I did know people.”
