Here are four things to watch for in Saturday's debate in Des Moines between the three remaining Democratic presidential candidates. It starts at 9 p.m. and will be aired on CBS.
1. How do the candidates address events abroad that raise major concerns about national security?
The terrorist attacks throughout Paris on Friday night have left at least 129 people dead. It is not yet confirmed who the attackers were or if they were affiliated with ISIS or other radical Islamic groups — though ISIS has claimed responsibility and the French government laid the blame there.
Steve Capus, an executive at CBS helping plan the debate, told the New York Times "there is no question that the emphasis changes dramatically." He suggested Saturday's debate will now have more emphasis on national security and foreign policy than previously planned.
The Paris attacks come on the heels of several other important international events since the last Democratic debate, which was held on Oct. 13.
The Oct. 31 downing of a plane en route to St. Petersburg, Russia after taking off from Egypt (another ISIS claim of responsibility) has raised concerns about airline security, as the British government and some congressional Republicans have said the crash was likely an act of terrorism. (U.S. government officials have not confirmed the plane's downing was terrorism, but also not ruled out that possibility.)
On Friday morning, U.S. and British officials said they believed that an airstrike had killed Mohammed Emwazi, a member of ISIS who had beheaded Western hostages in videos that were seen all over the world.
A greater focus on foreign policy will be a big change in the Democratic presidential primary. While much of the debate in the GOP 2016 field has been about foreign affairs, Clinton and her primary rival, Vermont Sen. Bernie Sanders, up to now have largely focused the struggles of middle-class Americans because of wage stagnation.
Clinton's words about the attacks in Paris will be particularly important. Because of her lead in the Democratic primary and the scrambled Republican field, Clinton is currently the most likely person to succeed Barack Obama as president. And she of course served as secretary of state from 2009-2013.
Clinton will be speaking as a longtime American policymaker and a potential president, trying both to explain to Americans what is happening abroad and reassure them another Sept. 11-style attack can be prevented.
2. Will Bernie Sanders attack Hillary Clinton?
In the run-up to Saturday's debate, Sanders had suggested he would look to more sharply attack Clinton, the front-runner.
In the first Democratic debate, perhaps the most significant moment was when Sanders downplayed the controversy over Clinton's use of a private e-mail account as secretary of state, arguing voters wanted to discuss real policy issues. Sanders' move won him plaudits among many Democrats, but also absolved Clinton of one of her biggest vulnerabilities.
The terrorist attacks in Paris will change the tone of the debate and therefore will affect Sanders' ability to engage with Clinton. He may feel it is inappropriate to blast Clinton sharply in a debate that will be much more serious in tone than past ones on either the GOP or Democratic sides. And Sanders is most passionate and versed in speaking about the economy. It's not clear he has the ability to lay out a better vision than Clinton about how the U.S. should handle complicated situations abroad.
Clinton voted for the Iraq War in Congress, which Sanders opposed. His usual tact on foreign policy is to cast himself as dovish, while Clinton is generally more supportive of military intervention than many liberal Democrats. But in the days after a terrorist attack, Clinton's approach may resonate more with voters.
3. How does Clinton discuss her role in some of the failures of U.S. foreign policy?
The rise of ISIS happened largely after Clinton left the State Department in early 2013. And it's not clear that any U.S. policy decisions could have prevented the emergence of the organization.
That said, the Obama administration has struggled to come up with strong policy responses to the conflict in Syria, the interventions of the Iranians and Russians in Syria to back a regime the U.S. opposes, and the military gains ISIS has made throughout the Middle East. And Clinton was one of Obama's chief advisers when the Syrian civil war started and as a candidate has praised Obama's decision-making.
Clinton has in the past suggested she did not agree with Obama's policies on Syria, favoring an earlier intervention on behalf of the rebels fighting the Assad government. But does Clinton have any unique proposals now for how to end the civil war there? Is she willing to more forcefully criticize Obama on foreign affairs issues, most notably his downplaying of ISIS early in 2014? If her influence on the president's actual decisions was limited, as she has hinted on Syria policy, how much should voters value her experience as secretary of state?
4. How do the candidates handle the racial debate happening on college campuses?
The controversies over racial issues that have divided the campus at Yale and led to the resignation of the University of Missouri's president introduce a new issue into the campaign. Some, even on the left, are wary of what they view as a climate in which black activists are trying to silence those disagree with them.
African-Americans, both on these campuses and nationally, argue the students are highlighting long-standing issues of racism. Yale's black students, for example, are calling for renaming a dorm on campus that honors John C. Calhoun, who was a strong defender of slavery as a South Carolina U.S. senator and vice-president during the middle of the 19th century.
All three of the Democratic candidates have aligned themselves with the "Black Lives Matter" movement. But would Clinton, who attended Yale's law school, support removing Calhoun's name from the dorm? Do the candidates agree with FBI director James Comey, who has suggested police are wary of doing their jobs after a year of protests of the behavior of some officers?