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Moses told the elders, “Stay here and wait for us until we come back. Aaron and Hur are here with you. If anyone has a dispute while I am gone, consult with them.”

Then Moses climbed up the mountain, and the cloud covered it. And the glory of the Lord settled down on Mount Sinai, and the cloud covered it for six days. On the seventh day the Lord called to Moses from inside the cloud. To the Israelites at the foot of the mountain, the glory of the Lord appeared at the summit like a consuming fire.

Then Moses disappeared into the cloud as he climbed higher up the mountain. He remained on the mountain forty days and forty nights. ...

When the people saw how long it was taking Moses to come back down the mountain, they gathered around Aaron. “Come on,” they said, “make us some gods who can lead us. We don’t know what happened to this fellow Moses, who brought us here from the land of Egypt.” So Aaron said, “Take the gold rings from the ears of your wives and sons and daughters, and bring them to me.”

All the people took the gold rings from their ears and brought them to Aaron. Then Aaron took the gold, melted it down, and molded it into the shape of a calf. When the people saw it, they exclaimed, “O Israel, these are the gods who brought you out of the land of Egypt!” Aaron saw how excited the people were, so he built an altar in front of the calf. Then he announced, “Tomorrow will be a festival to the Lord!”
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(Exodus 24.14-18, 32.1-5 NLT)

Aaron was clearly the second in command. And in Moses' absence, he was the leader in charge. He knew that the Lord had called Moses and he knew he was supposed to wait for Moses to come down.

And yet he so easily wavered. He chose not to lead as the Lord had called him to.

If we are ever entrusted to lead others, let us remember not to be like Aaron.