Is there a sadder Torah sight than Aaron standing by helplessly while the children of Israel build a golden calf?
When Moses went up the mountain, he left Aaron and Hur (Aaron's nephew) in charge, but Hur is not mentioned in this sidrah. The Talmud suggests that Hur had been killed as he attempted to appease an angry crowd, frantic at Moses's absence (Sanhedrin 7a).
Aaron feared he might suffer the same fate if he tried to challenge the people and the charge of murder as well as idolatry would be brought upon them.
The Talmud presents Aaron as unconcerned for his own welfare, and Rashi builds a case for Aaron trying everything to stop the calf from being built, playing for time and even constructing the calf himself in order to exonerate the people.
This is the kindest explanation for his neither rebuking nor attempting to dissuade them.
When Moses comes down from the mountain, he asks Aaron what happened. Aaron's answer, comments Rabbi Joseph Telushkin, surely ranks alongside "the dog ate my homework" as the flimsiest of excuses: Aaron threw the gold into the fire and it ... just... emerged as a calf!
There is a curious innocence about Aaron. This sidrah is often used as a proof-text for the unsuitability of Aaron as leader; he is simply not tough enough. Yet when Aaron dies, and we are told how deeply the people mourn him, they do not hold the golden calf incident against him.
We will never know whether the people would have listened if Aaron had asked them not to build the golden calf. One could not imagine Moses hanging back in such a situation. Being loved was not enough to qualify Aaron as a leader, but that love was great enough to overcome the collective memory of him as the witness - or even the misguided architect - of the people's greatest communal disaster. Love wins.