Useful idiot

In political jargon, a useful idiot is a derogatory term for a person perceived
as propagandizing for a cause without fully comprehending the cause’s goals, and
who is cynically used by the cause’s leaders. The term was originally used
during the Cold War to describe non-communists regarded as susceptible to
communist propaganda and manipulation. The term has often been attributed to
Vladimir Lenin, but this attribution is unsubstantiated.