Since last month, when five Democrats participated in their first primary debate, the field has winnowed to three -- Hillary Clinton, Bernie Sanders and Martin O'Malley. In the intervening month Vice President Joe Biden also decided he would not run for president. Now, going into the second Democratic debate, Clinton's lead has grown -- a CBS News/New York Times poll released Wednesday shows that 52 percent of Democratic primary voters across the U.S. support her, compared with 33 percent for Bernie Sanders and 5 percent for Martin O'Malley.

With Friday's attacks in Paris, the debate will shine a light specifically on foreign policy differences among the candidates and strategies to fight extremist groups abroad.

"Last night's attacks are a tragic example of the kind of challenges American presidents face in today's world and we intend to ask the candidates how they would confront the evolving threat of terrorism," CBS News Washington bureau chief Chris Isham said.

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CBS News' Nancy Cordes, who is covering the Democrats and will also be a debate moderator Saturday, and CBS News Senior Political Editor Steve Chaggaris say there are a few other key things they'll be looking for on the stage during this second debate for the Democrats.

Who will Hillary Clinton go after?

Cordes points out that in the Republican debate earlier this week, GOP candidates mostly directed their fire at Hillary Clinton, rather than at one another. Will Clinton similarly look beyond the Democratic field toward the Republicans in the race?

How will she fend off attacks from her Democratic opponents?

Martin O'Malley has already signaled he will be going after her record, although in the last debate she defused his attempt to cast doubt on her foreign policy prescriptions by reminding him that he himself had endorsed her for president in 2008, the last time she ran.

Will Sanders be able to criticize Clinton without sounding too harsh?

One of the tenets of Sanders' campaign has been that he would not run a negative campaign, and he has traditionally avoided negative attacks on his opponents in his prior campaigns. His senior strategist, Tad Devine, told CBS News' Hannah Fraser-Chanpong that Sanders would be ready to defend his ideas, but he had no plans to throw the first punch.

Will Sanders try for a do-over on the question of Clinton's emails?

Sanders' most memorable moment during the first Democratic debate came during a discussion of Clinton's email controversy. "People are sick and tired of hearing about your damn emails," he told Clinton on stage. While unintended, he handed Clinton a gift by appearing to make the very argument her campaign has made.

Can Clinton appeal to younger voters?

The CBS News/New York Times poll found that Sanders has an edge among younger Democratic voters with 46 percent, compared to 40 percent for Clinton. They don't vote as reliably as older voters, but they do have enthusiasm. How will Clinton work to convince them she's the candidate for tomorrow?

What is Martin O'Malley's pitch?

This will be a big audience for O'Malley, and he's likely looking for an opportunity to break out. Will he take a more aggressive stance? It's a risk for both O'Malley and Sanders, since Clinton is very popular with primary voters, and should he take that approach, he risks alienating those voters, Chaggaris suggests.

CBS News Chief White House Correspondent Major Garrett will be looking to see to what degree Sanders and O'Malley suggest that Clinton's authenticity is an open question, given the shift in her positions on issues ranging from trade to war.

Who and what is driving the discussion on social media?

Hillary Clinton and foreign policy have been driving the conversation on Twitter ahead of the debate. According to Twitter's data, 41 percent of the conversation related to the Democratic debate is focused on foreign policy and 33 percent is connected to national security as a result of the deadly terrorist attacks in Paris on Friday. Clinton has also been the most searched candidate on Saturday on Google.

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