Found an interesting site for you:
http://www.ushmm.org/wlc/en/article.php?ModuleId=10005267
U.S. officials could only have granted visas to the St. Louis passengers by denying them to the thousands of German Jews placed further up on the waiting list. Public opinion in the United States, although ostensibly sympathetic to the plight of refugees and critical of Hitler's policies, continued to favor immigration restrictions. The Great Depression had left millions of people in the United States unemployed and fearful of competition for the scarce few jobs available. It also fueled antisemitism, xenophobia, nativism, and isolationism. A Fortune Magazine poll at the time indicated that 83 percent of Americans opposed relaxing restrictions on immigration. President Roosevelt could have issued an executive order to admit the St. Louis refugees, but this general hostility to immigrants, the gains of isolationist Republicans in the Congressional elections of 1938, and Roosevelt's consideration of running for an unprecedented third term as president were among the political considerations that militated against taking this extraordinary step in an unpopular cause.
Roosevelt was not alone in his reluctance to challenge the mood of the nation on the immigration issue. Three months before the St. Louis sailed, Congressional leaders in both U.S. houses allowed to die in committee a bill sponsored by Senator Robert Wagner (D-N.Y.) and Representative Edith Rogers (R-Mass.). This bill would have admitted 20,000 Jewish children from Germany above the existing quota.
Where were all of these Republican supporters of Jews then?