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PHILADELPHIA (CNN) — Hillary Clinton “felt sad” watching a Republican National Convention that was mostly about “criticizing me,” she said an interview aired Sunday night on CBS’ “60 Minutes.”

“I seem to be the only unifying theme that they had,” the presumptive Democratic nominee said. “There was no positive agenda. It was a very dark, divisive campaign. And the people who were speaking were painting a picture of our country that I did not recognize — you know, negative, scapegoating, fear, bigotry, smears. I just was so — I was saddened by it.”

It was the first joint interview that Clinton and her new choice for the vice presidential nomination, Sen. Tim Kaine of Virginia, have conducted since Clinton introduced Kaine on Saturday in Miami.

Clinton complained of a “Hillary standard” — suggesting that she faces more scrutiny than other top-level politicians.

“I often feel like there’s the Hillary standard and then there’s the standard for everybody else,” she said.

Asked to explain that, Clinton cited “unfounded, inaccurate, mean-spirited attacks with no basis in truth” which “take on a life of their own,” pointing to Republicans’ criticism at the party’s convention in Cleveland last week.

“And for whatever reasons — and I don’t want to try to analyze the reasons. I see it. I understand it,” she said. “People are very willing to say things about me, to make accusations about me that are — I don’t get upset about them anymore, but they are very regrettable.”

In the interview, Clinton was asked what she calls Trump, in response to his moniker for her: “Crooked Hillary.”

“I don’t call him anything. And I’m not going to engage in that kind of insult fest that he seems to thrive on,” Clinton said.

“So whatever he says about me, he’s perfectly free to use up his own air time and his own space to do. I’m going to talk about what he’s done, how he has hurt people in business time after time after time,” she said.

Kaine, the Virginia senator and former governor who held his first joint rally with Clinton on Saturday in Miami, credited Clinton with letting “water go off her back on this.”

“That’s not the way I feel. When I see this, you know, ‘Crooked Hillary,’ or I see the, ‘Lock her up,’ it’s just ridiculous. It is ridiculous,” he said, referring to chants that broke out repeatedly at last week’s Republican National Convention in Cleveland.

Kaine added: “It is beneath the character of the kind of dialogue we should have, because we’ve got real serious problems to solve. And look, most of us stopped the name-calling thing about fifth grade.”

In the interview, Clinton also offered more details on her pledge to make sure the “middle class will not get a tax increase,” defining the “middle class” as those who earn less than $250,000 per year.

She said she’d never use a private email server in the White House, and admitted she’d erred by using one as secretary of state.

“Absolutely. I made a mistake. I should’ve had two accounts; one for personal and one for office. And I didn’t, and I take responsibility for that,” she said.

Kaine, for his part, described himself as a “utility player.” Clinton joked that he “plays a mean harmonica.”

Asked if he is ready to be president, Kaine said: “I’m ready first to be a supportive vice president so that the presidency of Hillary Clinton is is a fantastic one. But if something were to put that in my path, as much as any human being would be ready, I’d be ready.”