Kamala Harris commanded the first debate against Donald J. Trump, flashing her prosecutorial skills to leverage every chance to get under the former president’s skin in a 90-minute clash of visions and style.

They disagreed fiercely on abortion and the economy, immigration and the war in Ukraine. But throughout the night, Mr. Trump found himself in a defensive crouch, relitigating his record rather than picking apart hers.

The contrast was apparent even on mute. She smiled. He glowered. He spoke more, but she dictated the terms of the evening.

Here are six takeaways from a debate that was a remarkable reversal from June, when Democrats were so despondent they changed candidates afterward:

Harris set traps. Trump leaped into them.

Ms. Harris strode across the room to deliver the first handshake in a presidential debate since 2016. It was the first time she had met Mr. Trump in person, and she was intent on introducing herself: “Kamala Harris,” she said, as he took her hand. “Have fun,” he instructed her.

She sure appeared to. He did not.

Ms. Harris dominated the proceedings from nearly the start. She laid bait. He took it. It began with her needling Mr. Trump that his bored supporters had been leaving his rallies. It continued with her comment that he had inherited riches from his father. And on it went as she invoked his Republican critics, including those who served in his administration.