Anti-Semitism may have played a part in the fact that the US did not want to enter WWII right away. It is certainly true that anti-Semitism was present in the US. However, that was not at all the major reason for the delay.
First, we must remember that the war was not really about Jews. It was known that the Germans were persecuting Jews, but it is not as if the French and British were fighting for that reason. Therefore, it would not have made sense for the US to hold back out of anti-Semitism.
Second, and more importantly, US isolationism came out of WWI, not out of anti-Semitism. Isolationists in the US did not believe that any war in Europe could really represent a threat to the US. They did not want to get involved in another war like WWI for what they saw as no good reason.
By far the main reason for the late US entry into WWII was a desire to avoid entanglement in another European war that did not have a direct impact on US interests.