Launching 59 cruise missiles at a Syrian military airfield in response to a Syrian chemical weapons attack that killed dozens of civilians raises important questions. Does the president have, or should he have, the authority to use military force without the explicit consent of Congress?

The U.S. Constitution makes the president the commander-in-chief of the armed forces, while granting Congress the power to declare war. The framers of the Constitution intended through the latter provision to make Congress the principal decision-maker regarding the initiation of military campaigns. But they also sought to allow presidents some leeway with respect to the handling of crises.

REUTERS/Kevin Lamarque

During the first century and a half of U.S. history, most wars involving the United States – including the War of 1812, the Mexican-American War, the Spanish-American War, World War I and World War II – were backed by a congressional declaration of war. More recently, Congress authorized the Persian Gulf War and the post-Sept. 11 wars in Afghanistan and Iraq. Although Congress did not formally declare war in these three cases, an authorization of the use of force has held the same legal standing as a declaration of war.

But in the past 70 years, it has become quite common for American presidents to order combat operations without an explicit congressional endorsement. Presidents have maintained that their commander-in-chief power under the Constitution gives them the right to do so. Members of Congress have been split on this question.

In the wake of the recent missile strikes against Syria, congressional leaders of both parties endorsed the strikes, while other lawmakers argued Trump needed congressional approval.

Who’s right?

A precedent for presidents

President Harry Truman began the post-World War II trend away from congressional approval in 1950, when he deployed the military to repel North Korea’s invasion of South Korea. Truman argued that congressional authorization was unnecessary since the intervention had been endorsed by the United Nations Security Council.

Fifteen years later, Congress gave a green light to military action against Vietnamese Communist forces by passing the Gulf of Tonkin Resolution. However, President Richard Nixon declined to withdraw all U.S. troops from Vietnam when Congress repealed this resolution in 1970.

In 1973, Congress attempted to restrain presidents from engaging in prolonged conflicts without congressional assent by enacting – over Nixon’s objection – a law called the War Powers Resolution. The law stipulates that the president can only keep military forces deployed in “hostilities” for up to 60 days – with the possibility of a 30-day extension – without a congressional war declaration or use of force authorization.

No subsequent U.S. president has accepted the constitutionality of the War Powers Resolution, and presidents have continued to order military operations without congressional approval. In 1983, President Ronald Reagan deployed troops to Grenada to overthrow a repressive Marxist regime. In 1995 and 1999, President Bill Clinton ordered air strikes against Bosnian Serb and Serbian forces to prevent ethnic cleansing in Bosnia and Kosovo, respectively. None of these operations were authorized by Congress.

In 2011, President Barack Obama ordered air strikes against the military and government of Libyan dictator Muammar Qaddafi. This air campaign lasted about seven months, even though Congress had not endorsed it. The Obama administration argued that the operation was not bound by the War Powers Resolution’s 60-day limit because the absence of U.S. troops on the ground in Libya meant the U.S. had not entered into hostilities.

Obama also launched the U.S. military campaign against the Islamic State (IS) without gaining direct congressional assent for the campaign. In this case, the administration maintained that the campaign was covered by Congress’ 2001 authorization targeting individuals responsible for the Sept. 11 attacks and its 2002 authorization of the use of force against Iraq.

Congress’ end of the bargain

Congress, for its part, has contributed to the lack of constitutional clarity concerning some military operations by declining to vote on whether to authorize them. For three years, legislation has been pending before Congress that would provide direct authorization for the use of force against IS. Yet, congressional leaders have not brought this legislation to the floor of the House or Senate. In such contexts, the argument for a president acting unilaterally becomes all the more reasonable.

In the end, the United States will be best served if the president is granted discretion to deploy the military without congressional approval when quick action is needed to address a grave security threat or imminent humanitarian disaster. But Congress should weigh in directly on any deployments that might be long-lasting and carry major costs. By following this model, American leaders would stay true to the basic vision of the founders, while recognizing important distinctions among military operations in their urgency, importance and risks.