During the contentious political debate of 1787, Montesquieu enjoyed exceptional prestige in the United States. In their struggle against the Constitution adopted in Philadelphia, Anti-Federalists appealed to The Spirit of the Laws as their leading authority. In response, those defending the proposed Constitution had to go back to Montesquieu’s founding theories to counter the arguments of their opponents. Building upon previous scholarship, this article will explore three aspects of The Federalist’s political doctrine where Madison and Hamilton analyzed and subverted Montesquieu’s ideas: first, the dogma that republics cannot survive when surrounded by empires if they do not unite their forces in a Confederation; second, that in a federative state as in any kind of state, power should limit power; third, that in this constitutional arrangement, an independent judiciary should play a special role. Thus, the core of American federal ideology was borrowed from Montesquieu: that multiple layers of government could legitimately exist within a single polity, and that such an arrangement is not a defect to be lamented but a virtue to be celebrated if the balance of powers is properly respected. Yet, it is only by confronting the Anti-Federalists’ intellectual allegiance to axioms of The Spirit of the Laws that Madison and Hamilton were able to provide the first political treatise – however unfinished it might be – on the viability of modern democracies.