Donald Trump said Tuesday that recently released FBI documents proved that Hillary Clinton "fails to meet the minimum standard for running for public office," as both presidential candidates tried to appeal to military and retired voters in Southern swing states.

At a rally in Greenville, N.C., Trump said Clinton's use of a private email server for her correspondence while secretary of state was "disqualifying," a pointed escalation of his case against the Democratic nominee.

"It’s clear from the FBI report that Hillary Clinton lied about her handling of confidential information," said Trump, who added, "This is like Watergate, only it's worse."

Late last week, the FBI published scores of pages summarizing interviews with Clinton and her top aides from the recently closed criminal investigation into her use of a private email server in the basement of her New York home.

The summaries revealed that the FBI identified 13 mobile devices associated with Clinton's two phone numbers, but the Justice Department was unable to obtain any of them. On another occasion, an aide to former President Bill Clinton recalled "two instances where he destroyed Clinton's old mobile phones by breaking them in half or hitting them with a hammer."

"Who uses 13 different iPhones in four years?" Trump asked rhetorically Tuesday. "People who have nothing to hide don't destroy phones with hammers. They don't ... destroy evidence to keep it from being publicly archived as required under federal law."

Earlier Tuesday, Clinton accused Trump of insulting America's veterans and pressing dangerous military plans around the globe.

Clinton, addressing supporters in Florida, warned that Trump would lead the nation back to war in the Middle East. And to military vets and their families, she pointed anew to his summertime dust-up with the Muslim parents of a slain American soldier.

“He called the military a disaster,” Clinton said. “He said, ‘I know more about ISIS than the generals do' ... His whole campaign has been one long insult to all those who have worn the uniform."

She also vowed to help the military by giving it the proper equipment to “dismantle terror networks” and providing members and ex-members with better mental-health care.

In response, Trump touted a letter from 88 retired generals and admirals citing an urgent need for a "course correction" in America's national security policy. At his evening rally, the real estate mogul suggested that he would rely on the generals to make up for his own lack of national security inexperience to take on ISIS. He vowed to give military leaders a "simple instruction" soon after taking office: "They will have 30 days to submit to the Oval Office a plan for soundly and quickly defeating ISIS."

Clinton pushed back, saying Trump has lagged in securing key military supporters compared to past Republican nominees including John McCain and Mitt Romney. She pointed to her endorsements from retired Marine Gen. John Allen, who blasted Trump at the Democratic National Committee, and former CIA deputy director Mike Morell.

Trump also also extolled a new CNN/ORC poll that shows him leading Clinton 45-43 percent in a four-way race with Libertarian Gary Johnson at 7 percent and Green Party’s Jill Stein at 2 percent.

The numbers are a stark reversal from mid-August, when Clinton led by roughly 8 percentage points.

“As for polls, I don’t pay much attention,” Clinton told reporters Tuesday on her new campaign jet en route to Tampa for her only event of the day.

The Democratic nominee said she is instead focusing on what she calls Trump’s un-American views on dictators, illegal immigrants and religious tolerance.

“So dark, so divisive, so dangerous,” Clinton said in Tampa. “I want to be a president who brings a country together. I’m glad that [running mate] Tim Kaine and I are running a campaign of issues, not insults.”

The conflicting messages came as the candidates prepared to appear at an MSNBC forum Wednesday night on national security. While they will appear separately and not be on stage at the same time, it could serve as a warm-up to their highly-anticipated first presidential debate on Sept. 26 at New York's Hofstra University.

Meanwhile, Clinton's campaign released a new television ad entitled, "Sacrifice," showing military veterans watching some of the New York businessman's more provocative statements.

The spot includes clips of Trump claiming to know more about ISIS than military generals, and his criticism of McCain, the Republican senator from Arizona and a former prisoner of war. The ad, which features former Georgia Sen. Max Cleland, a triple-amputee who served in Vietnam, also keys on Trump's assertion that he has sacrificed a lot compared to families who have lost loved ones in conflict.

"Our veterans deserve better," reads a line at the end of the ad, which is airing in Ohio, Florida, Iowa, Nevada and Pennsylvania.

Clinton spent much of late August fundraising in such wealthy enclaves as Hollywood and the Hamptons -- for the TV ads, state-level operations and other campaign expenses needed in the final 62 days of the White House race.

She raised a combined $143 million in August for her campaign, along with the Democratic National Committee and state parties -- her best month yet.

Clinton began September with more than $68 million in her campaign's bank account to use against Trump, who has not yet released initial fundraising totals for August.

Clinton on Monday used a campaign plane for the first time this election cycle, a Boeing 737 with about 100 seats for passengers and crew.

She has since taken serious questions at least twice from reporters flying with the campaign, in an apparent attempt to quell criticism that she avoids the news media and has not held a full-fledged press conference in 276 days, arguments the Clinton camp disputes.

Trump flies in a private jet, while his press corps travels in a separate one. The wealthy businessman on Monday allowed reporters on his plane, which he said lacks such accommodations, but vowed to occasionally continue taking questions onboard.

FoxNews.com's Joseph Weber and The Associated Press contributed to this report.