Useful idiot
A person, especially in a public position, who is easily persuaded and manipulated by other people for their own purposes and goals.
In political jargon, a useful idiot is a derogatory term for a person seen as a tool of propaganda for a cause without a full comprehension of the cause and its goals.
The term has often been attributed to Vladimir Lenin, but there are no official documents to confirm it.
English by Vesna 