FDR also went after Andrew Mellon who the treasure secretary under Coolidge. Bad move , not only was Andrew rich ,but as a man who once headed the IRS he knew exactly what he was doing and FDR couldn’t touch him. Perhaps the signal FDR wanted to send was that nobody was immune from his tyranny.
Mellon was not only the Treasury secretary under Coolidge but also under Harding before him and Hoover after him. He can be thought of as the father of what later become known as "supply side economics."