To attack a narcissist, you need to attack the cracks in the reality they paint for themselves.
It just so happens that as someone who has been an enthusiastic and professional grade debater for 40+ years, Harris also knew exactly how to do this without getting his mud on herself, and she knew to do it just as he was hoping to hit his stride.
It was great to watch. So many politicians from so many walks of life have been completely humiliated by Trump's ridiculous persona. He's so inflammatory, so full of lies, and so narcissistic professional politicians have been reduced to flinging his poo back at him. Instead Harris made him wallow in it.
Not here in Minnesota. Thanks Mr. Walz!