Regarding Hitler, I think he tapped in to a racist, anti-Semitic feeling in Germany at the time. Their economy was to some extent dominated by Jewish financiers. By harping on about it, and whipping up the population to desire the removal of Jews, he built on this racism, using 'Aryan stereotypes' to reinforce it, until The Final Solution was tacitly accepted. He then proceeded to promote the creation of a Roman Empire-type Reich, which obviously appealed to the people, as they embraced it wholeheartedly, and armed for War with enthusiasm.

Parallels can be seen today. A politician can only persuade his/her adherents to believe what they already have in their minds.
I don't think it's hypnotism so much as opportunism.

In Cote d'Ivoire recently, President Gbagbo took power by tapping into the people's despair at their poverty, and the corruption rife among the rulers. He didn't hypnotise them so much as promise them vast improvements. Sadly, he was extremely corrupt himself, and the poverty merely continued or increased. Luckily, he was eventually booted out after a civil war.