"3. The Constitution was written to be understood by the voters; its words and phrases were used in their normal and ordinary as distinguished from technical meaning; where the intention is clear, there is no room for construction and no excuse for interpolation or addition." --United States v. Sprague, 1931.
No offense but you need a better example regarding FDR & SCOTUS as he wasn't POTUS in 1931. His time in office was 1933 to 1945. Also, his plan to pack and expand SCOTUS with leftist justices to fifteen from nine, wasn't announced until 1937, February 5, 1937 to be exact. But this blatant power grab by FDR was too much even for democrats in Congress and it went nowhere, thank God.
Thank you for your concern about the order of events, but I believe that I have stated the order of events correctly.
I wasn't around at the time, but the PC idea of Supreme Court infallibility with respect to interpreting the Constitution probably became prevalent after FDR's activist majority justices wrongly widened the scope of Congress's Commerce Clause powers from the bench with their decision in Wickard v. Filburn in 1942. This was more than ten years after United States v. Sprague was decided, Constitution-respecting justices noting the relatively simple language of the Constitution in the Sprague opinion.