Ray, the Supreme Court has been interpreting the law since Marbury Vs Madison, 1803. It’s their job
A couple famous examples
Dred Scot, where the Supreme Court interpreted the law to insist that “the negro had no rights a white man was bound to respect.” Dred Scott invalidated state laws abolishing slavery–as Lincoln wrote, "We shall lie down pleasantly, dreaming that the people of Missouri are on the verge of making their State free, and we shall awake to the reality instead, that the Supreme Court has made Illinois a slave State.” Illinois had banned slavery–the Dred Scott case made it illegal to abolish slavery.
Plessy vs Ferguson, 1896, in which the Supreme Court interpreted this amendment to the constitution, #15:
Section 1. The right of citizens of the United States to vote shall not be denied or abridged by the United States or by any State on account of race, color, or previous condition of servitude."
to mean that it was ok to legally segregate and disenfranchise based on color.
The idea that “interpretation” is something FDR invented is, sorry, completely preposterous.