There are two sides to every story. If Presidents did not have immunity and he had not died in office FDR could have faced a plethora of charges for his time in office.
For your thesis I’d hope and expect you did some research on the purported ‘other side.’ It’s been a decade since I read Malkin’s book. I can’t recall all her specific purported evidence, although I do recall an interesting tale of one of the Pearl Harbor raiders. Who was shot down and parachuted onto Hawaii (possibly a different island, I forget) where he murdered some civilians before being caught. My remembered overall impression was there was a lot more reason to suspect bad actors within the Japanese community than popularly claimed. Just as over the years I’ve seen several things that make me suspect FDR was NOT surprised by Pearl Harbor and wanted the attack to happen, but expected a much more palatable casualty total. The shocking reality resulted in a huge coverup of probably the worst charges FDR could have faced.