Everybody in Pennsylvania wants Trump, you know,” he said. “We get crowds like this everywhere.” He boasted of a rally planned for Florida with an expected 25,000 people.

As he spoke, Katie Packer, a strategist for Mitt Romney in 2012, posted a photograph on Twitter of 30,000 people at an Ohio rally four years ago a week before Mr. Romney’s defeat. “None of the Trump crowds so far in the general election surpass what we regularly had in ’12,” Ms. Packer wrote. “They are so naïve.”

Yet Mr. Trump whipped the crowd to anger at the news media and its “crooked” polls. At one point, he falsely claimed that CNN had turned off its live coverage as he was accusing the network of manipulating a debate-night focus group. The crowd then chanted an anti-CNN epithet.

He also read the results of unscientific, opt-in online surveys.

“Trump 70, Clinton 30,” Mr. Trump quoted from a reader survey by the Drudge Report on which candidate had won the second debate. “Oh, listen to this,” he said, reading from an iPhone. “Time magazine. You think Time magazine likes me?” He cited the result: 89 for Trump, 11 for Clinton. “Oh, here’s a good one,” he added. “Well, they’re slightly conservative — Breitbart. 93 to 7,” he read.

Mr. Trump’s supporters who were waiting to hear him speak cited alternative sources of information they preferred, dismissing even Fox News in favor of emails from far-right commentators like Allen B. West, a former congressman, and Dennis Lynch, who makes films about illegal immigration.