Franklin Roosevelt and Huey Long were very similar Progressive Democrats in that they were both economic Progressives who believed in things like infrastructure investment funded by the public and making American capitalism work for more people. But there were several differences in the two and they mostly resulted around character.
Franklin had a lot of it and wasn’t a corrupt man or a corrupt politician looking to become some dictator over the United States. Huey was exactly that, but a dictator over Louisiana first as Governor where he basically ran the whole state under his leadership and when he left the Louisiana governors mansion to serve in Congress as a Senator, he was still running Louisiana.
But now Huey Long as a U.S. Senator had more national power and since these two men were similar ideologically at least on economic-policy, President Roosevelt saw Senator Long as a threat to his leadership and power and someone who needed to be put down. But Huey Long would’ve gone down anyway because of his lifestyle and how he carried himself in office.