And Moses said unto Aaron, What did this people unto thee, that thou hast brought so great a sin upon them?

Wesley's Notes

32:21 What did this people unto thee - He takes it for granted that it must needs be something more than ordinary that prevailed with Aaron to do such a thing? Did they overcome thee by importunity, and hadst thou so little resolution as to yield to popular clamour! Did they threaten to stone thee, and couldest not thou have opposed God's threatenings to theirs?

Matthew Henry's Concise Commentary

32:21-29 Never did any wise man make a more frivolous and foolish excuse than that of Aaron. We must never be drawn into sin by any thing man can say or do to us; for men can but tempt us to sin, they cannot force us. The approach of Moses turned the dancing into trembling. They were exposed to shame by their sin. The course Moses took to roll away this reproach, was, not by concealing the sin, or putting any false colour upon it, but by punishing it. The Levites were to slay the ringleaders in this wickedness; yet none were executed but those who openly stood forth. Those are marked for ruin who persist in sin: those who in the morning were shouting and dancing, before night were dying. Such sudden changes do the judgments of the Lord sometimes make with sinners that are secure and jovial in their sin.