Every president who has tried to bend the Federal Reserve to his will has encountered the same wall: an institution whose independence is not a courtesy but a legal and structural fact. Donald Trump, now in his second term, is learning this lesson again, as the chairman he personally selected resists calls for interest rate cuts in order to contain inflation born of geopolitical upheaval. The conflict is ancient in its shape — political power pressing against institutional constraint — and its resolution will say something lasting about the durability of American economic governance.