As his prominence grew in Germany and his fears of Hitler's reign coming to fruition, he earned the sponsorship of Rabbi Stephen Wise who was a close adviser to President Franklin Roosevelt. In 1937, Prinz immigrated into the United States, after giving a farewell sermon attended by thousands, including Adolf Eichmann. He immediately began lecturing throughout the U.S. for the United Palestine Appeal, established in the 1920s as the fund raising arm in the United States for the Jewish Agency for Israel. It was, essentially, the precursor to what became the American Jewish support base for a nation state of Israel and the United Israel Appeal.