Former Sen. Joe Lieberman, who served as Democrats' vice presidential nominee in 2000, explained the three moments that matter when someone becomes a nominee for vice president.

On Wednesday during  “The Brian Kilmeade Show,”  he explained those three moments are the announcement day, the acceptance speech at the Democratic National Convention and the vice presidential debate.

He was told the same thing when he was picked to run for vice president with former Vice President Al Gore in 2000.

Lieberman made the comments after Sen. Kamala Harris, the politically shrewd California senator with a law enforcement background that has caused some tensions with the progressive left, was announced as Joe Biden's running mate.

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“Right now she looks fresh, she’s a different generation obviously from Joe Biden so she puts it together, but she’s … in the arena now in what’s going to be a real no-holds-barred campaign,” he told host Brian Kilmeade.

Lieberman acknowledged that he thinks some of her past comments, including remarks on Biden’s alleged inappropriate behavior with women, “will be a problem and she’ll have to figure out how to handle it and not seem like she’s changing where she was.”

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Harris once said that she believed women who accused Biden of inappropriate touching.

“I believe them and I respect them being able to tell their story and having the courage to do it,” Harris said at the time.

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Kilmeade asked Lieberman if comments made by Harris, including those reacting to Biden's accusers, are big or small problems?

“It will be a medium-sized problem,” Lieberman said. “I mean it’s ultimately up to the people, but I presume that the Trump campaign is ready to bring up those tapes and she’ll have to explain it and put it in context.”

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Lieberman said his first reaction to hearing Biden chose Harris as his running mate was “positive,” adding that he’s “reacting as somebody who is still a Democrat, but sort of hanging on sometimes by the tips of my fingers.”

He noted that Harris is “more to the center-left” compared to “some other choices that were much further out,” adding that he “was pleased about that.”

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Among the other Black candidates Biden was thought to be considering were Rep. Val Demings of Florida, who is a former Orlando police chief; Atlanta Mayor Keisha Lance Bottoms; former Georgia House leader and 2018 gubernatorial nominee Stacey Abrams; former U.S. ambassador to the U.N. under President Obama Susan Rice; and Rep. Karen Bass of California.

Lieberman said Harris has “a good record.”

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“She was attorney general and I think she handled herself well,” he continued, adding that “she’s been in the arena and this is going to be a real tough campaign.”

Harris is ready for a tough campaign, and she showed that during the primary campaign, he said.

Lieberman said he believes Harris will likely face criticism from both sides, but that her left-wing detractors will likely be "stifled" by their overriding desire to unseat the president.

He went on to say “it will go back to her record as a prosecutor in which she was pretty tough and it’s not the kind of stuff that some of the protesters today are happy with.”

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 Fox News’ Adam Shaw, Paul Steinhauser and Alex Pappas contributed to this report.