The first, and most obvious, difference: There was no international conspiracy of German Jews in the 1930s attempting to carry out daily attacks on civilians on several continents. No self-identifying Jews in the early 20th century were randomly massacring European citizens in magazine offices and concert halls, and there was no “Jewish State” establishing sovereignty over tens of thousands of square miles of territory, and publicly slaughtering anyone who opposed its advance. Among Syrian Muslims, there is. The vast majority of Syrian Muslims are not party to these strains of radicalism and violence, but it would be dangerous to suggest that they do not exist, or that our refugee-resettlement program need not take account of them.
On a related note, the sympathies of Syrian Muslims are more diverse than those of Nazi-era German Jews. A recent Arab Opinion Index poll of 900 Syrian refugees found that one in eight hold a “to some extent”-positive view of the Islamic State (another 4 percent said that they did not know or refused to answer). A non-trivial minority of refugees who support a murderous, metastatic caliphate is a reason for serious concern. No 13 percent of Jews looked favorably upon the Nazi party.