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SACRAMENTO, Calif. — Donald Trump unleashed a withering personal attack on Hillary Clinton on Wednesday, saying she has “no natural talent” and was “one of the worst secretaries of state in the history of our country.”

The presumptive Republican presidential nominee, whose campaign remarks are usually off-the-cuff, came prepared to attack his rival after Clinton called him a "fraud" for taking "advantage" of Americans through Trump University.

With Clinton due to deliver an aggressive policy speech Thursday that will attempt to spell out why he is unfit for the presidency, the Republican candidate issued a preemptive strike.

Trump told a sweltering California crowd in 90-degree heat Wednesday night that he had seen an advance copy of Clinton’s remarks and alleged her soon-to-come statements on his foreign policy plans were “lies.”

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Keeping cool thanks to an air conditioner at his podium, Trump derided Clinton as “weak.”

“She's one of the worst secretaries of state in the history of our country,” he said. “Now she wants to be our president? Look, I'll be honest, she has no natural talent to be president.”

Secrets of the campaign trail: this air-conditioner behind @realDonaldTrump podium today. pic.twitter.com/PwQE16q5MH — Ali Vitali (@alivitali) June 2, 2016

He told the crowd: "All you have to do is watch her speak. And you ever notice, even for a minor speech she has teleprompters. Do I have teleprompters here?”

The answer Wednesday night was no — though Trump has used prompters for prior speeches.

Trump didn't address ongoing reports of fraud and legal battles regarding Trump University, focusing on spelling out Clinton's weaknesses.

He cited Libya, Iran, Iraq and refugees in making his case — and even said that another Democrat would be a better option.

"Honestly, I tell you what folks, she doesn’t know what the hell she’s doing. It’s going to be another four years of disaster. We’re probably better off with Bernie," he told the crowd.

Related: Bill Clinton Defends Against GOP's 'Relentless Personal Attacks'

On Libya, Trump raised the issue of Benghazi, saying: “Remember the famous phone call? At three o'clock in the morning she'll answer the call. Guess what? She was sleeping. She was sleeping like a baby. ‘Don't wake me up.’ Of course she took the calls from her slimy friends but she didn't take 5-600 calls.”

He continued: "At the same time Secretary Clinton was surrendering our jobs to China, the Chinese government and its supporters were funneling huge sums, I mean huge sums of money to Bill Clinton so that he'd give speeches. So she's given China all these deals and China's paying him vast amounts of money to make speeches? Great job."