A demagogue is a leader who makes use of popular prejudices, false claims and promises in order to gain power by pandering to fear and emotions to shut down reasoned deliberation.
Though separated by more than 200 years of history, Alexander Hamilton defined the character of a demagogue like Trump when he wrote on August 18, 1792:
“The truth unquestionably is, that the only path to a subversion of the republican system of the Country is, by following the prejudices of the people, and exciting their jealousies and apprehensions, to throw affairs into confusion, and bring on civil commotion…
“When a man unprincipled in private life, desperate in his fortune, bold in his temper, possessed of considerable talent…despotic in his ordinary demeanor — known to have scoffed in private at the principles of liberty — when such a man is seen to mount the hobby horse of popularity — to join in the cry of danger to liberty — to take every opportunity of embarrassing the General Government & bringing it under suspicion — to flatter and fall in with all the nonsense of the zealots of the day — It may justly be suspected that his object is to throw things into confusion that he may ‘ride the storm and direct the whirlwind.'”
Be warned, America. History is a powerful judge of character.