When asked whether she would drop out of the presidential race if she is indicted because of this usage, Clinton became uncharacteristically exasperated.
"Oh, for goodness – it's not going to happen," she said, after reiterating that none of the emails sent over her private server were marked as classified at the time. "I'm not even answering that question."
Clinton, 68, was also asked to address a recent poll showing that only 37 percent of Americans consider her honest and trustworthy.
"Obviously, it's painful for me to hear that," she said. "I have very much committed, to the best of my ability, my energies to helping people. I will continue to do that, to demonstrate by my past actions and levels of commitment and plans that people can count on me."
She added: "I am not a natural politician like my husband and like President Obama ... I can just hope that people see that I am fighting for them and that I can improve their lives."
Clinton also went head-to-head with Vermont Senator Bernie Sanders over several issues, most notably that of their respective immigration policies. Although they were each attacked for their past voting records on immigration bills, both promised that they would not deport undocumented immigrant children or undocumented immigrants without criminal records.
"I am committed to introducing comprehensive immigration reform and a path to legitimate citizenship within the first 100 days of my presidency," Clinton said. "My priorities are to deport violent criminals, terrorists or anyone who threatens our safety."
After hearing the story of an immigrant from Guatemala whose husband was deported, leaving their five children fatherless for more than three years, Sanders, 74, explained his own immigration policy.
"The essence of what we are trying to do is to unite families, not to divide families," he said. "The idea that a mother is living here and her children are on the other side of the border is wrong and immoral. I will do everything I can to unite your family."
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In contrast to their strong feelings about immigration reform, when asked outright whether Republican presidential candidate Donald Trump is a racist, both Clinton and Sanders shied away from giving too harsh of an answer.
"People can draw their own conclusions about him, but I will just end by saying this: You do not make America great by getting rid of everything that made America great," Clinton said, condemning his actions as "un-American" and "not at all in keeping with American values."
Sanders added: "The American people are never going to elect a president who insults Mexicans, who insults Muslims, who insults women, who insults African-Americans."
The debate comes on the heels of Sanders' surprising win in Tuesday's Michigan primary. Although Clinton has won almost twice as many delegates as Sanders so far, the tables could still very well turn in Sanders' favor. 857 delegates will be at stake when Florida, Ohio, Illinois, North Carolina and Missouri voters all cast their ballots on March 15, and states like Idaho, Utah, Arizona, Alaska, Washington, Hawaii, Wisconsin and Wyoming, all of whom will host primaries and caucuses in the next month, "look quite strong" for Sanders, according to FiveThirtyEight's Nate Silver.