Hillary Clinton said she can "absolutely" guarantee Democratic voters that her use of a private email account while secretary of state will not derail her campaign.
"Before it was emails it was Benghazi, and the Republicans were stirring up so much controversy," Clinton said during the MSNBC Democratic debate on Thursday.
Last week the State Department declared that 22 emails from Clinton's private server had been marked "top secret" and would not be released. The emails were not marked classified at the time they were received.
"This is beggers the imagination. I have absolutely no concerns about it," Clinton added.
NBC News reported Thursday that State Department officials determined classified information was sent to the personal email accounts of Secretary of State Colin Powell and the senior staff of former Secretary of State Condoleezza Rice. Both served under Republican President George W. Bush.
Bernie Sanders has avoided criticizing Clinton on her email use, notably saying last fall that the American people were tired of hearing about her "damn emails."
Sanders repeated Thursday that he would continue to avoid attacking Clinton on the issue.