He got elected democratically. In the German system, one party gaining the absolute majority is very rare and coalition governments are the norm. The cancellor is usually the candidate of the party with the largest percentage in that coalition. In the case of the NSDAP, that was Hitler. The conservatives formed a coaltion with him because they were sure the conservative president would be able to keep Hitler in check. Unfortunately, said president did the opposite and was instrumental in giving Hitler absolute power.

Donald Trump just won with a plurality of around 31% of eligible voters

Then Hitler somehow convinced the center right President to grant him powers

Class interests are how. Hitler came to power by promising big business interests that he would crush labor unions and socialists and promote the interests of capitalists, which he largely did. The term "privatization" was first used to describe the Nazi economy. Many of these rich Nazi collaborators survived and thrived under the Nazis (so long as they weren't part of a minority), and also survived its fall. The company that manufactured Zyklon B, for example, eventually became part of the company now known as Bayer. The rich accepted fascism as a calculated risk because the country was in crisis and there was a risk of communists coming to power and redistributing their wealth.