Why did Antoine Arnauld argue that Descartes’s proof of God’s existence was circular?

The argument that René Descartes’s proof of God’s existence is circular, famously identified by Antoine Arnauld as the Cartesian Circle, centers on a logical dependency between God and clear and distinct perception.1

Descartes argues that he can only be certain of his clear and distinct ideas because a perfect, non-deceiving God exists to guarantee their truth. However, to establish the existence of this God, Descartes relies on his own clear and distinct perception of the arguments for God's existence.12

Arnauld and other critics pointed out that this creates a circular dependency:
* The validity of clear and distinct perception depends on the existence of God.12
* The proof for the existence of God depends on the validity of clear and distinct perception.12

Consequently, Descartes appears to assume the truth of the very criterion he is attempting to validate through his proof of God.12