When President Trump authorized a strike to capture Venezuela’s president, Nicolas Maduro, without congressional approval, it was the latest manifestation of the increasingly common belief by presidents that they have broad unilateral authority when it comes to military operations. The Constitution’s original meaning, however, belies this notion. As I have developed at more length here, the Constitution’s “declare War” clause allocates to Congress—and by implication denies to the president—the power to initiate hostile military action against foreign nations. That was the eighteenth-century meaning of “declaring war”: to initiate a state of war, which could be done by proclamation or by hostile military action. This meaning was expressed by a wide range of interpreters in the founding era and widely assumed to be the constitutional rule in the immediate post-ratification period.
Although “declaring” war may seem to suggest a formal pronouncement, by the eighteenth century, such formalities were often ignored (as Alexander Hamilton noted in Federalist #25). Instead, eighteenth-century writers said that war could be “declared” by actions as well as formalities. The great Swiss international law authority Emer de Vattel, for example, wrote in 1758 that “when one nation takes up arms against another, she from that moment declares herself an enemy to all the individuals of the latter, and authorizes them to treat her as such.” John Locke wrote in the previous century that the “State of War” could be “declar[ed] by Word or Action.” Professor Saikrishna Prakash has demonstrated extensive use of “declare” in this way in the period immediately before the Constitution’s drafting.
Because declaring war could be done by word or action, the Constitution’s declare war clause put the power of war initiation entirely in Congress. Leading commentators in the ratification period and immediately afterward consistently recognized this allocation. In the Pennsylvania ratifying convention, for example, framer James Wilson said of war powers:
This system will not hurry us into war; it is calculated to guard against it. It will not be in the power of a single man, or a single body of men, to involve us in such distress; for the important power of declaring war is vested in the legislature at large: this declaration must be made with the concurrence of the House of Representatives: from this circumstance we may draw a certain conclusion that nothing but our national interest can draw us into a war.