Like his predecessor in office, President Trump has sent the U.S. military into combat without Congress' blessing. Just as President Barack Obama launched an air war in Libya and sent troops to support Syrian rebels, Trump struck Damascus to punish it for gassing its own people. For its troubles, the Trump administration has come under fire from liberals and conservatives for seizing Congress' power to declare war.

In this case, Trump has the Constitution about right. Throughout our history, neither presidents nor Congresses have waited for a declaration of war before conducting hostilities. We have used force abroad more than 100 times, but declared war only five. Presidents have unilaterally sent forces to battle Indians, Barbary pirates, and Russian revolutionaries; North Korean and Chinese communists; Marxist guerrillas in Latin America; and tyrants in the Balkans and the Middle East. Presidential initiative, followed by congressional acquiescence, spans administrations of both parties back to Abraham Lincoln, Thomas Jefferson, and George Washington.

If the issue is health care or taxes, Congress enacts policy first, and the president implements it. But with national security, the framers gave the president the lead. As Alexander Hamilton wrote in the Federalist Papers: "The direction of war implies the direction of the common strength, and the power of directing and employing the common strength forms a usual and essential part in the definition of the executive authority."  Presidents should conduct war because they could act with "decision, activity, secrecy, and dispatch." Hamilton famously wrote: "Energy in the executive is a leading character in the definition of good government. … It is essential to the protection of the community against foreign attacks."

Foreign affairs are unpredictable and involve the highest of stakes. They demand swift, decisive action best carried out by a unified branch of government. In order to forestall another 9/11 attack, or take advantage of a window of opportunity to strike enemies, the president needs flexibility. Congressional control can lead to passivity, isolation, and worse decisions, all at the price of speed and secrecy.

Congress does not have a proud track record running our national security. After rejecting the Treaty of Versailles at the end of World War I, Congress kept the United States out of Europe at a time when democracies fell and fascism grew. As Europe and Asia plunged into war, Congress passed neutrality acts to keep the United States out. While critics worry about presidential adventurism, the real threat to our national security could come from inaction.

Presidential critics commonly invoke the American Revolution for support: Surely the rebels against King George III would not give the president much authority. It is true that the revolutionaries rejected the royal prerogative, and they created weak executives at the state level. But when the framers wrote the Constitution in 1787, they rejected these failed experiments and restored an independent, unified chief executive post with its own powers in national security and foreign affairs.

Despite the record of practice and the Constitution's institutional design, critics nevertheless argue that we should radically remake the American way of war. They typically base their claim on Congress' power to "declare war." But these observers read the 18th-century constitutional text through a modern lens by interpreting "declare war" to mean "start war." When the Constitution was written, however, a declaration of war served diplomatic notice about a change in legal relations between nations. It had little to do with launching hostilities.

Our Constitution sets out specific procedures for passing laws, appointing officers, and making treaties. There are none for waging war because the framers expected the president and Congress to struggle over war through the national political process. Other parts of the Constitution, properly read, support this reading. Article I, Section 10, for example, declares that the states shall not "engage" in war "without the consent of Congress" unless "actually invaded, or in such imminent danger as will not admit of delay." This provision creates exactly the limits desired by presidential critics, complete with an exception for self-defense. If the framers had wanted to require declarations of war, they could have just extended Section 10 to the executive.

Presidents, of course, need congressional cooperation to succeed. Only Congress can raise the military, which gives it the power to block, delay, or modify war plans. Since World War II, Congress has authorized and financed our large standing military, one primarily designed to project power worldwide. If Congress disagrees with the president, it can simply refuse to fund the war. During the fight over the Constitution's adoption, James Madison responded to predictions of presidential militarism: "The sword is in the hands of the British king; the purse is in the hands of the Parliament. It is so in America, as far as any analogy can exist." Congress ended America's involvement in Vietnam by using its power of the purse.

The Constitution creates a presidency that can respond forcefully to prevent serious national security threats. Presidents can take the initiative, and Congress can use its funding power to check presidents. Instead of demanding a legalistic process to begin war, the framers left war to the struggle between the branches. As we confront the new challenges of terrorism, rogue nations, and WMD proliferation, now is not the time to introduce sweeping, untested changes in the American way of war.

John Yoo, coauthor of "Striking Power: How Cyber, Robots, and Space Weapons Change the Rules for War," will join a panel discussing "War Powers and the Constitution" at 6:30 p.m. Wednesday at the National Constitution Center. To register, visit or call 215-409-6700.