The difference is clear: wartime powers. Even though war had not been declared, the US was already ramping up. I think he had plenty of legal precedents to grant asylum, not immigration. Difference.
Well... let's remember first that FDR actually believed he was doing more than, in fact, he was, due to misleading numbers fed to him by the State Department.
Significant numbers purportedly of refugees allowed in were in fact only those put on lists for some future immigration.
Second, during the war, when FDR's war powers supposedly increased, a few hundred Jewish refugees were granted asylum, transported and held in a concentration camp... in upstate New York!
Yes, from our perspective, it was pathetic, but it was the best they could do, at the time.
Finally, given today's chaotic border-immigration conditions, it's hard to remember that once upon a time, the US had serious laws which were strictly enforced.
So, the Left's assault on FDR here is really an assault on those laws -- they say FDR should have ignored the law then, just as Obama ignores such laws today.
So, if we respond: FDR should have broken the laws then, but Obama should enforce them today, then we're forced to set criteria by which any President should or should not follow the Constitution's requirements.
And that path leads to insanity...