Hardly,, as FDR was the Commander in Chief, had the US lost FDR's name would be mud...Beat the Japs and the Nazi's all at once...Worst US President ever - by far.
No, the military beat the Japs and Nazis all at once. FDR wisely rubber-stamped whatever they wanted.
You can thank Marshall for the American victory in WWII. When FDR and his acolytes were strangling the US military it was Marshall who ensured that the brightest minds were placed in the most appropriate positions to prepare for the inevitable war that he knew was coming thanks to the progressives lack of diplomatic skills to keep Hitler et al under control.
Marshall, more than any other person is responsible for the USA's victory in WWII and the elevation to super power.