SAN FRANCISCO (CBS NEWS) — Hillary Clinton says she wasn’t watching the Republican convention, but she heard about the chanting from the convention floor to “lock her up, lock her up,” which was a response to the decision of the Justice Department not to charge her for mishandling classified information because she used a private email server while she was secretary of state.

Clinton, who appeared with her running mate, Virginia Gov. Tim Kaine, told CBS News’ Scott Pelley that it just made her “sad” about what it said about the Republican campaign.

“I seem to be the only unifying– theme that they had,” she said. “There was no positive agenda. It was a very dark, divisive campaign.” The negativity, “fear, bigotry, smears” saddened her, she said in the interview, which aired Sunday on “60 Minutes.”

One of the issues that has been difficult for Clinton to shake is that of her private email server — she promised it wouldn’t be a mistake she’d make twice. Clinton reiterated that she set it up because “it was recommended that it would be convenient, and I thought it would be. It’s turned out to be anything but.” And she told Pelley, “I’ll tell ya one thing, that is one lesson I have learned the hard way, and there will not be any such thing in the White House.”

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