There were a number of things the candidates had to do--explain how they would enact policies that best evidenced their vision of how to improve our nation, express their connection to Americans' everyday issues, and seem presidential, which means not being an emotional need-hole and not being a lying garbage person.
Hillary Clinton managed to pass this not especially rigorous test of being a competent human who made no ridiculous demands on the credulity of her hearers, and developed answers that showed a knowledge of history, continuity, fairness, Constitutionality, and made statements that necessarily degraded the alleged competencies of her opponent.
Trump failed to demonstrate that he understood the issues better than Secretary Clinton, or had exceedingly better policies, or could even refute claims that his business acumen was not great and that he was not necessarily a racist. Within the debate, she lobbed truthballs at his silver spoon start, his many bankruptcies, his settlement in a claim against his properties for race discrimination in the 1970's--and frankly, she only hit him on the tip of his particular amoral iceberg.
She had him sputtering, and it did not help that he was snorting and sniffling--a cold perhaps?Or Bolivian marching powder? So 80's and Lifestyles of the Louche and Loathesome! But whatever--the funny old thing is, she beat him on facts. She knew her shit. He appeared to be rambling and repetitive and spoke like a toddler.
He needs to bone up or bow out--and it's too late to bow out.