"I love it," she told a dinner in Iowa on August 14, 2015, noting she had opened an online account with Snapchat, which deletes posts automatically. "Those messages disappear all by themselves."
The crack scored a laugh from the audience, but the issue was plenty serious. About a month earlier, news broke of an FBI investigation into whether some of the emails that passed through Clinton's unsecured server contained classified information.
But hacked emails of John Podesta, Clinton's top campaign official, show the Democratic candidate and her team were slow to grasp the seriousness of the controversy, initially believing it might blow over after one weekend.
It did not, and became the most recent example of a penchant for secrecy that has fuelled questions about Clinton's trustworthiness, which she has acknowledged has been a political challenge.
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The joke was included in hacked emails WikiLeaks began releasing earlier this month, saying they included years of messages from accounts used by Podesta. Podesta warned that messages may have been altered or edited to inflict political damage, but has not pointed to any specifics.
In a series of emails on March 3, 2015 the same day The Associated Press called for comment staffers tossed around the idea of making jokes about the emails at a dinner hosted by EMILY's List, a political action committee, that evening.
"I wanted to float idea of HRC making a joke about the email situation at the EMILY's List dinner tonight," Jennifer Palmieri, director of communications for Clinton's campaign, wrote at 2:37 PM, using the candidate's initials.