My guess is that FDR had little sympathy for the Nationalists. However, he also did want to start a war in the Democratic party. Some history here is quite relevant. Wilson allied with the UK in WWI. Irish Democrats and German Democrats never forgave him. In the subsequent elections, Republicans easily won, in part because of profound disunity in the Democratic party (the Great Depression sent the Republicans into the wilderness later). Were there other reasons for Republican ascendancy in the 1920s? Of course, there were.

Back then, upscale urban liberals were only a small force in the Democratic party (for example, Elanor Roosevelt). Of course, they would have supported the Republicans to the hilt. Conversely, relatively downscale Catholics were a huge force and they had an opposite view.

Another factor was that the US was still quite isolationist. US isolationism was strongly reinforced by the debacle of WWI (political and economic debacle, not military). No less that FDR held off on getting the US involved before Pearl Harbor. Even after Pearl Harbor, FDR called for declaration of war only against Japan (not Japan and Germany). Germany solved that problem by declaring war on the US.