http://en.wikipedia.org/wiki/History_of_antisemitism_in_the_United_StatesFrom Wikipedia:
American attitudes towards Jews[edit]
Antisemitism in the United States was also indicated by national public opinion polls taken from the mid nineteen thirties to the late nineteen forties. The results showed that over half the American population saw Jews as greedy and dishonest. These polls also found that many Americans believed that Jews were too powerful in the United States. Similar polls were also taken, one of which posed that 35-40 percent of the population was prepared to accept an anti-Jewish campaign.
In a 1938 poll, approximately 60 percent of the respondents held a low opinion of Jews, labeling them “greedy,” “dishonest,” and “pushy.”[23] 41 percent of respondents agreed that Jews had "too much power in the United States," and this figure rose to 58 percent by 1945.
In 1939 a Roper poll found that only thirty-nine percent of Americans felt that Jews should be treated like other people. Fifty-three percent believed that "Jews are different and should be restricted" and ten percent believed that Jews should be deported.[24] Several surveys taken from 1940 to 1946 found that Jews were seen as a greater threat to the welfare of the United States than any other national, religious, or racial group.[25]
Although only 0.6 percent of the nation's 93,000 commercial bankers in 1939 were Jewish,[citation needed] the idea that Jews controlled the banking system remained a popular myth. Political antisemitism also was high during the war years, with 23 percent of respondents in one 1945 survey saying they would vote for a congressional candidate if the candidate declared "himself as being against the Jews" and as many as 35 percent saying it would not affect their vote. Jews also noted the influence of antisemitism when the U.S. State Department opposed efforts to lower immigration barriers to admit Jews and other refugees fleeing the Holocaust and Nazi-occupied Europe.
Thus, antisemitism was fairly widespread in the U.S, a sentiment which reduced the inclination of Americans to help the Jews in Europe.