Useful idiots are people who are incapable of independent thought. They act solely on emotion and then in response to what they are told they should feel by the ruthless revolutionaries pulling the strings.
This mayor is 100% useful idiot. Totally governed by feeling. Lose a chunk of you city to revolutionaries? 'Aww, that's so cute! they just want what we all do, equality and friendship for all! Wait, they're shooting each other? Well uh, um, uh, it was an accident?'
Both variations are mean as hell.