Answer
The plea for clemency served as the catalyst for Desmoulins' downfall, as it enraged Robespierre and led him to perceive Desmoulins as a threat to the revolution's unwavering ideology. Robespierre, driven by his unwavering devotion to the revolution's principles, viewed Desmoulins' plea for leniency as a dangerous departure from the revolutionary path, ultimately resulting in Desmoulins' demise.