After two days of policy-focused addresses with modest crowds, former President Donald J. Trump returned to form on Wednesday with an outdoor speech in North Carolina, where he insisted that he would not give up personal attacks on Vice President Kamala Harris and continued to sow doubts about the integrity of the election in November.

Speaking to thousands of supporters outside a hangar at an aviation museum in Asheboro, N.C., Mr. Trump ridiculed his advisers for pressuring him to focus on policy instead of on personal insults as he mocked President Biden’s physical appearance. He called former House Speaker Nancy Pelosi “crazy,” labeled Ms. Harris both “stupid” and a “Marxist or a communist” and said former President Barack Obama was “nasty.”

And as he promised to invest in America’s military, criticized the Biden administration’s foreign policy and vowed that only he could restore world peace, Mr. Trump repeatedly revived his false claims of widespread election fraud in 2020 and spun them forward to November.

As he insisted that he could end the war in Ukraine just by being elected, Mr. Trump portrayed his victory as a forgone conclusion that could be stymied only by electoral fraud.

“When, if, but when — I have to always say ‘if,’ you know, because they cheat,” Mr. Trump said of Democrats. “I would say ‘when’ if they didn’t cheat, but they cheat. That’s the one thing — they’re great at cheating in elections.”

The gathering in Asheboro was Mr. Trump’s first outdoor rally since he survived an assassination attempt at an event in Pennsylvania last month. There were numerous heightened security precautions. The lectern where Mr. Trump was speaking from was partially surrounded by bulletproof glass. At least five uniformed personnel, several with sniper rifles, were on surrounding rooftops. And large storage containers were stacked up to block a clean view of the stage from a distance.