Lindbergh saw the creation of the German Air Force firsthand, something President Roosevelt did not, though the US Embassy in Berlin did request Lindbergh collect intelligence. You are correct about the sentiment in the US being by and large against entering the war, and the reasons were understandable. It wasn't FDR who directed the attention to Lindbergh's antisemitic remarks, he didn't need too, the press was not shy in covering it. Frankly, FDR had more important things to worry about, and Lindbergh hurt himself with this own words.