What did Hitler promise to do to those who opposed him?

The Nazi party’s policies were deliberately vague so they might appeal to as many people as possible. People of both right and moderate-left wing politics joined because they agreed with at least one of their policies:

an aim to abolish the "unfair punishment" of the Treaty of Versailles was popular with many Germans
promises of better pensions and increased employment appealed to the common man and many traditional socialists
opposition to communism led many landowners and businessmen to support the Nazis – they were seen as the only credible right-wing alternative to the left-wing parties.
belief in the supremacy of the German race appealed to nationalists.
paramilitary groups reminded people of the comradeship they shared as soldiers during World War One
the promise to re-militarise Germany would bring in huge industrial contracts – bringing support from many industrialists
Hitler's hatred of Jews struck a chord with many people - they were a convenient scapegoat for all Germany's problems

The idiot who could play like a donkey!