Exodus 32:21 - Ellicott's Commentary On The Whole Bible

Moses said unto Aaron, What did this people unto thee ? — The second step was to inquire how the idolatry came about; and here Moses very reasonably addressed himself to Aaron. Aaron had been left in charge of the people (Exodus 24:14), to advise them, direct them, control them, if necessary. How had he acquitted himself of this charge? He had allowed the people to commit a great sin. What excuse could he offer for his conduct? Had the people injured him in any way? The question is asked ironically.