When you realize someone you had respected has lost their mind you would refer to them as "Robespierre coming down the mountain" in reference to Robespierre's Cult of the Supreme Being festival in which he appeared at the top of a 'paper mache' mountain constructed in the center of Paris in a toga and decended to give a speech. Many saw this as proof that he thought he was more than human and had lost touch with reality.
"Oh, here's Robespierre coming down the mountain!"
by The Real Honeybear May 4, 2009