CINCINNATI, Ohio -- Facing new questions about her use a private email server as Secretary of State, Hillary Clinton moved forward on Monday with her campaign’s plan to paint her Donald Trump as a man too erratic and too divisive to be president.

“I am running against a man who says he doesn’t understand why we can’t use nuclear weapons,” she said at a campaign rally at Kent State University. “He actually said, ‘Then why are we making them?’ And he wants more countries to have nuclear weapons -- Japan, South Korea, even Saudi Arabia -- imagine nuclear weapons smack in the middle of the Middle East.”

She quoted President Ronald Reagan, saying he feared “some fool or some maniac or some accident triggering” nuclear war.

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“That has been the fear and the commitment of Democratic and Republican presidents since the dawn of the Atomic Age,” she said. “So, that would he think about Donald Trump, who says he wants to be, and I quote, ‘unpredictable’ about using the most powerful weapons ever produced?”

In a memo shared with news outlets on Sunday night, Robby Mook, Clinton’s campaign manager, laid out how Clinton, who will also travel to the battlegrounds of Florida, Pennsylvania and North Carolina by week’s end, will explain the “choice” between her and her opponent. In addition to national security, Clinton is expected to talk about her work on behalf of children and families and her economic vision.

“The choice is clear,” Mook wrote in the memo. “Americans deserve a president with the temperament and experience to tackle the issues facing our country and to work with all Americans to solve them, not a candidate who has proven himself time and again to be temperamentally unfit and unqualified to be President and Commander-in-Chief.”

Clinton did, however, acknowledge in both Kent and at another event later Monday in Cincinnati that some voters still have concerns about her reliance on a personal email address as Secretary of State. She reiterated that it was a “mistake” that she regrets, but Clinton was defiant, telling investigators that “by all means” they should continue their review.

CBS News learned on Monday that the FBI has started to sift through additional emails found on a laptop belonging to Anthony Weiner, the estranged husband of longtime Clinton aide Huma Abedin. Investigators are separating Weiner’s emails from Abedin’s emails and will work to determine whether or not any of them are pertinent to the agency’s probe into Clinton’s use of a private email server.

“I am sure they will reach the same conclusion they did when they looked at my emails for the last year,” Clinton said. “There is no case here.”

Later, as the sun set along the Ohio River in Cincinnati, Clinton vowed to “stay focused” on the voters and “the problems that keep you up at night.”

“That’s what this election is all about,” she said. “It’s not about the noise and the distractions. It’s about the kind of country we want...and what kind of president can help get us there.”