DES MOINES — The pack of cheering voters, sweating reporters and snapping cameras surrounding Joe Biden made its way through the Iowa State Fair like a pulsating amoeba, consuming everyone and everything in its path.

“Do you like being the front-runner?” a reporter shouted Thursday afternoon. “What about calling President Trump a white supremacist, like Senator Elizabeth Warren did?”

“You just want me to say the words so I sound like everybody else,” Mr. Biden said, a flash of anger in his voice. “I’m not everybody else. I’m Joe Biden. I’m staying the way I am.”

This summer has been full of predictions about an early Biden demise as a presidential candidate, be it from a poor debate performance or some gaffes, like his comment Thursday that “poor kids” are just as bright as “white kids.” But Mr. Biden has rebounded repeatedly, maintaining a commanding, crowd-drawing position in the contest.