On April 16, President Trump vetoed Senate Joint Resolution 7. Pursuant to the 1973 War Powers Resolution, the new statute directed the president to “remove United States Armed Forces from hostilities in or affecting the Republic of Yemen” — where they are assisting a Saudi-led coalition that is present with the consent of Yemen’s government — within 30 days. There was an exception for forces “engaged in operations directed at al Qaeda or associated forces.”

The veto was essential to upholding Trump’s oath of office to “preserve, protect and defend the Constitution.” Many, no doubt, voted “aye” because they honestly believe that Congress must approve all military operations and thus has the authority to remove forces from Yemen. But ignorance of the law is no excuse. If members of Congress believe the president’s foreign policies are misguided, they may communicate those concerns to him. But, with very limited exceptions largely involving treaties, nominations, and (now-illegal) all-out wars of aggression, legislators may not superimpose their own policy preferences over the constitutional discretion of the president to manage our foreign policy.

The veto was also correct as a policy matter. While some support for the statute was simply politically partisan, some was clearly intended to protest the Saudi murder of American journalist Jamal Khashoggi or to address the tragic humanitarian crisis in Yemen — arguably the greatest such crisis in the world today. But the statute would have rewarded Iran (which provides ballistic missiles and other support to Yemen’s Shiite Houthis, who hate Israel, Jews, and the United States, and admire Iran’s Hezbollah terrorists), undermined peace and stability in the region, and placed at risk one of the most important maritime chokepoints to international petroleum commerce. The Houthis have fired Iranian ballistic missiles at ships in the Red Sea, including at the U.S.S. Mason; and Major General Qassem Soleimani — commander of Iran’s elite Quds force — declared last July that Iran might use proxies to disrupt oil shipments through the strategically critical Bab el-Mandeb Strait. Most wise people hope the United Nations peace efforts will succeed, but removing a major incentive for the Houthis to compromise will not likely further that end.

In addition, the resolution defined the word “hostilities” to include “in-flight refueling of non-United States aircraft conducting missions as part of the ongoing civil war in Yemen.” Refueling operations by U.S. KC-135 and KC-10 tankers were ended last year in response to congressional pressure. That won’t keep coalition aircraft from striking targets and killing people anywhere in Yemen; but it will greatly reduce their loiter time over target — perhaps eliminating the time needed to make certain the assigned target is, in fact, a lawful military target rather than a wedding gathering or school bus filled with innocent children. (Enhanced loiter time is one of the many benefits of using drones to deliver ordnance against terrorists, as the pilot can delay the attack if he notices, for example, a group of children walking past the target.)

To its credit, Congress recognized that ceasing intelligence and logistical support for the Saudi-led coalition might well endanger the lives of American citizens in the region and increase the risk of terrorist attacks on U.S. Armed Forces and allies around the globe — and attacks on the continental United States as well. But rather than consider these critical issues before voting, Congress in its wisdom directed the president to submit “reports” on these other issues within 90 days — two months after the troops had been withdrawn and the damage done.

Separation of Powers and ‘Declaring War’ Under the Constitution

Raised on the writings of John Locke, Montesquieu, and William Blackstone, the Framers understood that when Article II, Section 1, of the Constitution vested the nation’s “executive Power” in the president, the foreign-relations power was the “essential element of the grant” (to quote the legendary University of Chicago professor Quincy Wright in his 1922 classic, The Control of American Foreign Relations).

As Secretary of State Thomas Jefferson explained in an April 24, 1790, memorandum to President Washington, the Constitution declares that “the Executive power” of the Nation is vested in the president, submitting only special articles to a “negative” by the Senate. Jefferson reasoned: “The transaction of business with foreign nations is executive altogether; it belongs, then to the head of that department, except as to such portions of it as are specially submitted to the Senate. Exceptions are to be construed strictly.”

Three days later, Washington recorded in his diary that he had discussed Jefferson’s memo with Chief Justice John Jay and Representative James Madison (often called “the Father of the Constitution”), and both agreed with Jefferson that most foreign-policy decisions were “Executive” in character and thus “vested in the President by the Constitution.”

Three years later, Jefferson’s chief rival in Washington’s cabinet, Treasury Secretary Alexander Hamilton, took an identical position in his first Pacificus essay when — after noting that the Constitution vested the “executive power” in the president — he wrote that “the power of the Legislature to declare war” was an “exception” out of “the general ‘executive power’ vested in the President,” and thus should be “construed strictly.” Relying upon the same authority, Federalist representative (and later Supreme Court chief justice) John Marshall declared in 1800: “The President is the sole organ of the nation in its external relations, and its sole representative with foreign nations. . . . He possesses the whole Executive power.” Marshall’s “sole organ” language has been quoted with favor in scores of Supreme Court cases over the decades.

Indeed, this understanding of presidential power was widely embraced by all three branches of government until around the end of the Vietnam War. For example, in a 1969 address at Cornell Law School, Senate Foreign Relations Committee chairman J. William Fulbright declared: “The preeminent responsibility of the president for the formulation and conduct of American foreign policy is clear and unalterable.”

Formal Declarations of War

One of the most misunderstood terms in constitutional law in the modern era is “Declaration of War.” On August 17, 1789, James Madison moved in the Constitutional Convention to narrow the power to be given Congress from “to make war” to the much narrower power “to declare war.” “Declare war” was a term of art from the Law of Nations, and was associated only with all-out aggressive wars — which were legal in the 18th century. As Hugo Grotius, often called the father of modern international law, explained in his 1620 treatise on The Law of War and Peace: “No declaration is required when one is repelling an invasion, or seeking to punish the actual author of some crime.”

Nor is such a declaration necessary when a country is using force inside the territory of another country with its consent, such as the current situation in Yemen; or against a non-state actor such as al-Qaeda, ISIS, or the Houthi in Yemen. Indeed, for Congress to formally “declare war” against ISIS or the Houthi would greatly strengthen their claims to be sovereign states. Those who demand new congressional authorization to fight ISIS ignore the fact that in 2001 Congress formally (but unnecessarily, since we were acting defensively) authorized the use of force against al-Qaeda, and the unanimous U.N. Security Council has repeatedly noted that ISIS is a “splinter group of Al-Qaeda.” (See, e.g., its resolutions 2170 and 2253.)

More fundamentally, the kind of total aggressive war historically associated with declarations of war was outlawed by Article 2(4) of the 1945 U.N. Charter, and no country has clearly issued such a declaration since World War II. Just as the power to grant “Letters of Marque and Reprisal” (authorizing private ship owners to capture enemy ships as “prize”) given to Congress in Article I, Section 8 became an anachronism when such instruments were outlawed in the 1856 Declaration of Paris, the power to “declare war” — given to Congress in the same clause — became irrelevant when the sorts of conflicts historically associated with the term were banned under international law (unless and until a president tries to launch one anyway).

The Founding Fathers understood the concept of force short of war. In the 1990 case of United States v. Verdugo-Uriquidez, the Supreme Court noted: “The United States frequently employs Armed Forces outside this country — over 200 times in our history — for the protection of American citizens or national security.” In contrast, Congress has declared war twelve times in five wars.

When President Jefferson learned that Barbary pirates might be planning to declare war against the United States, he dispatched two-thirds of the new U.S. Navy to the Mediterranean with instructions to sink and burn the pirates’ ships if, upon arrival, they learned war had been declared. Although the June 1, 1801, departure of the squadron was reported in newspapers, Jefferson did not formally notify Congress of his actions until his first State of the Union message on December 8. No one in Congress appears to have expressed concern the president had usurped legislative authority.

Congress does, of course, have other powers relevant to this conflict, including the requirement in Article I, Section 9, that no money can be drawn from the Treasury without appropriations made by law. Congress may refuse to appropriate new funds for the military, but the Supreme Court has repeatedly observed — most recently in the 2006 case of Hamdan v. Rumsfeld — that “Congress cannot direct the conduct of campaigns.” And it can no more “condition” appropriations to compel the president to exercise his constitutional discretion as directed by Congress than it can condition appropriations for the judiciary upon the Supreme Court deciding pending cases as instructed by Congress. Such a theory would destroy the separation of powers.

Senate Joint Resolution 7 was passed by the House by a vote of 247–175 and by the Senate 54–46. This strongly suggests the two-thirds vote needed in each chamber to override the veto is unlikely. That is a very good thing.