There was certainly some support for Hitler and the Nazis in the 30s in the US but it was not widespread, as, although it is estimated around 25% of Americans were of German decent, many had come in the mid 1800s and were very much assimilated. But even Germans who were born in, and even fought for Germany during WW1 would later go on to fight against them in WW2

In 1933 'Friends of New Germany' was established by of Nazi Deputy Führer Rudolf Hess and later became 'German American Bund' in 1936 after Hess called for the return of the leaders of 'Friends of New Germany' to the fatherland, apparently because they were creating a bad image of the Nazis with their activities .

This article is a good read but I'll give you a quote.

Bund created recreational camps such as Camp Siegfried in New York and Camp Nordland in New Jersey. It also established Camp Hindenburg in Wisconsin and the group met frequently in Milwaukee and Chicago beer halls. The Bund created an American version of the Hitler Youth that educated children in the German language, German history and Nazi philosophy. Although this organization tried to differentiate itself from the previously unsuccessful Friends of New Germany, the German Foreign Ministry commented that “In reality...they are the same people, with the same principles, and the same appearance”.

The organisation never really took off, with Nazi leaders in Germany saying that the leader, Fritz Julius Kuhn, spoke poor English, made questionable choices with money and was generally a poor leader.

A facade of swastikas and “Sieg Heil” prevailed, but in reality Kuhn was to become seen simply as an incompetent swindler and liar who spoke poor English; even the Nazis were embarrassed of him. German Ambassador Hans Dieckhoff called him “stupid, noisy and absurd”.

He was investigated by the New York district attorney and was arrested on charges of larceny and forgery, among other things that he admitted to. He was then stripped of his American Citizenship and then put in prison for being an enemy alien.

[During the war around 10,000 German-Americans were imprisoned as enemy aliens.] (http://www.economist.com/news/united-states/21642222-americas-largest-ethnic-group-has-assimilated-so-well-people-barely-notice-it)

TL,DR: A little support, but not much. As most German-Americans considered themselves more American than German, and the leaders of Nazi organisations in the US made poor decisions.