"That only flies if there was opposition to his policies from the right. There wasn't."
Very true. The Republicans at the time, lock, stock and barrel, refused to get America into the war AT ALL. Had Japan not attacked at Pearl Harbor, the Republican Isolationists were willing to allow Hitler to conquer Europe, which he probably would have but for American intervention.
FDR's turning back of the Liberty and denial of entry to Jewish Refugees was a bad things, no doubt about it. It sent people to their deaths. It was one of FDR's bad decisions. But FDR was, nevertheless, the American leader who saved Western civilization. Had the Republicans been in charge, the Germans would have been allowed to sweep Europe. They were NOT interested in getting involved, period. The 50 overage destroyers FDR rushed to Britain in the darkness of 1940 on Lend-Lease? Not forthcoming, and that alone might have made the U-Boat War against Britain decisive. Without Lend-Lease alone, never mind US troops and forces, the UK may very well not have survived. The USSR probably would not have survived. Without US intervention in Europe, the Nazis would have probably won. And had the GOP been running the show, there would not have been US intervention in Europe.
All true, in many ways the war resulted from a moral failure of Western civilization. At least until the invasion of Poland. For the US, even in the face of the destruction of Poland, we stayed out till attacked. The warning signs were there beginning with the persecution of early 1930s Germany.