Democrats argue over Islamic State fight after Paris attacks
The Democratic presidential hopefuls have clashed over how to deal with militant group Islamic State, in the wake of deadly terror attacks in Paris.
Hillary Clinton, speaking on a debate stage in Iowa, said "it cannot be an American fight" and called on Turkey and the Gulf states to do more.
But rival Martin O'Malley disagreed and said the US had to "stand up to evil" and lead from the front.
The attacks killed 129 people and injured hundreds in the French capital.
Hours after the near-simultaneous attacks on Friday, CBS News vowed to shift the focus of the debate to put more emphasis on counter-terrorism and foreign policy.
A moment's silence was observed in Des Moines before the debate began, and the three candidates expressed their condolences to the French people.
But then they clashed over the rise of IS, which has claimed responsibility for the atrocities.
Mrs Clinton, the former secretary of state, was challenged by Vermont Senator Bernie Sanders for backing the Iraq War, which he says led to the rise of the militants.
She disagreed, saying US foreign policy did not have the "bulk of responsibility" for the instability in the region, pointing instead to Syrian President Bashar al-Assad and Iraq's former leader, Nouri al-Malaki.
Analysis - Kim Ghattas, BBC News, Des Moines
This was a debate that was going to be focused on domestic policy but the attacks in Paris meant the first half-hour was dominated by foreign policy.
It was a discussion that Mrs Clinton as former secretary of state should have aced but she didn't. She seemed tense and on the defensive as her rivals and the moderators challenged her on record and Mr Obama's legacy.
While she demonstrated better knowledge and grasp of the issues, neither she nor her Democratic rivals really gave a detailed plan on how to defeat or contain the so-called Islamic State.
Mr Sanders and Mr O'Malley had clearly made a decision ahead of the debate that they would not play nice with the frontrunner this time.
This made the second Democratic debate feistier and more spirited but still civil. The road to the nomination is still close to impossible for the two men but they're not giving up.
IS cannot be contained, it must be defeated, Mrs Clinton said, adding that while American leadership was essential, "we will support those who take the fight to Isis [IS]".
But she and the other candidates did not spell out how far they would go.
The US has been part of a coalition of countries taking part in air strikes against IS in Syria and Iraq, but some of the Republican presidential candidates have called for the deployment of US ground forces.
In other debate highlights:
Mr O'Malley attacked "immigrant bashing" Republican Donald Trump's plan to build a wall on Mexico border
he and Mrs Clinton said the US should accept 65,000 Syrian refugees, far higher than the 10,000 coming
she backed a minimum wage of $12/hour, but Mr Sanders wants $15/hour
he criticised her for taking campaign donations from Wall Street
she replied that she supported New York City's financial sector to help it recover from the 9/11 attacks
Mr Sanders said he will make public college tuition free, paid for by raising taxes
This primetime showdown was the party's second debate of the election campaign, two fewer than the Republicans, who have a much wider field.
In 79 days, Iowa will be the first state to pick a presidential candidate from each party.
Voters across the US will go to the polls finally in November 2016 to choose the new occupant of the White House.