"one who will preach doctrines he knows to be untrue to men he knows to be idiots." H.L. Mencken
Mencken's definition of a demagogue is as apt today as it was early last century. I expect the ecstasy seen in some political gatherings today would be difficult to tell from that seen in crowds gathered at the Well of the Comitia in ancient Rome, listening to someone running for office as Tribune of the Plebs and promising a general cancellation of debt to all.
Of course, the crowds of ancient Rome were also known to stone a erstwhile politicians for not keeping campaign promises. Hmmmmm.