Hitler was a master politician and manipulator. In Germany in the 1930s people were out of work, poor, and desperate. They sought answers and solutions, and were very vulnerable and receptive to a skilled manipulator. Hitler told the Germans that the situation was not their fault, that the blame belonged to the Jewish bankers, that Jews had stabbed Germany in the back (regardless of the fact that many Jewish men died fighting for Germany in World War I), and that Germany could be restored to its past glory. He told them that they were the master race and all others should be their servants. The moderates and voices of reason were drowned out by extremists like Hitler. 

The victims of the Holocaust were somewhat surprised. Germany before Hitler wasn't the most anti-Semitic country in the world; the late 19th century had seen pogroms in Poland and Russia that caused millions to flee for the New World. Germany was one of the most modern, cosmopolitan and advanced societies in the world at the time. Jews were somewhat integrated. It was France that had experienced l'affaire Dreyfuss, not Germany. But unfortunately Germans were persuaded to go against people whom they had lived alongside for decades and fought alongside during the Great War. 

I hope we can learn from our mistakes in history and keep a healthy skepticism towards politicians, especially those who are particularly bombastic.