This piece was written in collaboration with three of my extraordinary students at the University of Chicago Law School: Sten Jernudd, Zachary Levine, and Daniel Scime.

Two weeks ago, President Donald Trump ordered a missile strike on an airfield in Syria. The missiles were not aimed at ISIS, nor did they target any al-Qaida-affiliated group. The strike was instead aimed at a Syrian missile base in response to the Assad regime’s recent use of chemical weapons against civilians. Then this Monday, Vice President Pence – standing near the DMZ in South Korea – proclaimed that the United States’ “era of strategic patience” with North Korea is over. Speculation has mounted that the Trump Administration might now be contemplating a preemptive strike.

Such speculation has laid bare one of our nation’s oldest and most vexing constitutional issues: To what extent does the Constitution grant the president the authority to employ armed force without congressional authorization? The debate over this question is as old as the Republic, but rather than clarifying the appropriate contours of presidential power in this realm, the passage of time has only obscured them.

Article I of the Constitution grants Congress the power to declare war, raise armies, maintain the navy, make rules governing the land and naval forces of the United States, call forth the militia, and control the expenditure of federal funds. Article II, on the other hand, provides that the president shall be the “Commander in Chief” of the military forces of the United States. Thus, at first glance, the division of powers is clear: Congress has the power to regulate the military and to declare war, and the president has the responsibility to command the military in the implementation of war.

With increasing frequency, however, presidents have unilaterally deployed American forces into hostile situations abroad without any congressional approval.

In practice, though, it has not been that simple. Congress has actually declared war only five times in our nation’s history – the War of 1812, the Mexican-American War, the Spanish-American War, World War I, and World War II. In many other circumstances, Congress has expressly authorized the use of force by enacting specific legislation. Examples of this phenomenon begin with the Quasi-War with France in 1798 and include more recently the Vietnam War and the use of American military force in Afghanistan and Iraq. With increasing frequency, however, presidents have unilaterally deployed American forces into hostile situations abroad without any congressional approval. It is this latter scenario that most clearly strains the constitutional system envisioned by the Framers.

Historically, the power of the executive to act unilaterally was reserved for purely defensive actions. President George Washington wrote in 1793, for example, that “no offensive expedition of importance can be undertaken until after [Congress has] deliberated upon the subject, and authorized such a measure.” In 1801, after sending naval ships to the Barbary Coast to protect American shipping against the Barbary pirates, President Thomas Jefferson made clear that he was “[u]nauthorized by the Constitution, without the sanction of Congress, to go beyond the line of defense.”

This distinction between offensive and defensive action has a certain logic to it. The president clearly has a responsibility to defend the nation against attack, and in moments of peril, delay can lead to serious harm. Prudence thus dictates that the president must have the authority to act decisively, when necessary, to ensure the safety of the country. Offensive military action, on the other hand, is not usually characterized by the same degree of urgency.

Over time, though, practical exigencies, political self-interest, and the difficulty of distinguishing offensive from defensive actions have frayed this distinction. As a result, presidents have increasingly assumed greater authority to decide themselves when, where, how, and to what extent the American military should be brought to bear overseas.

In the years since World War II, bi-partisan containment policies and a growing web of global alliances have increasingly led presidents to deploy force unilaterally. In Korea, for example, rather than seek congressional authorization, President Harry Truman justified his decision to deploy U.S. forces overseas by invoking treaty commitments to the United Nations’ Security Council. And well before the 1964 Gulf of Tonkin Resolution expressly authorized American military action in Vietnam, Presidents John F. Kennedy and Lyndon Johnson committed tens of thousands of U.S. troops to aid South Vietnam.

SAUL LOEB via Getty Images

In the wake of the Vietnam War, Congress enacted the 1973 War Powers Resolution over President Richard Nixon’s veto in order to restrict the president’s authority to act unilaterally. But the Resolution has done little to constrain the way in which presidents employ military force overseas. Although President Ronald Reagan sent American troops into Grenada and President George H.W. Bush sent American forces into Panama, neither bothered first to obtain congressional approval for their actions. Similarly, President Bill Clinton ignored Congress when he decided to order bombings in Kosovo in 1999, and President Barack Obama justified his action in Libya in 2011 by invoking the nation’s commitment to its NATO allies. In 2002, President George W. Bush’s Deputy Assistant Attorney General, John Yoo, went so far as to maintain that, given the president’s allegedly broad authority to direct the use of military force, “congressional authorization [for the invasion of Iraq was] legally unnecessary.”

Thus, over time, a succession of presidents have increasingly assumed near plenary power to order American forces into combat. Although the Constitution empowers only Congress to declare war, presidents now operate on the premise that they can use military force overseas whenever they think it appropriate.

The plain and simple fact is that there are reasonable arguments for dividing power in different ways.

Is this arrangement desirable? On one hand, the prevailing assumption of broad presidential power in this regard clearly departs dramatically from what the Framers of our Constitution conceived it to be. Broad presidential power circumvents the democratic principle that, absent a direct and immediate threat to the country, the national interest is best served when the representatives of the People have an opportunity to debate and decide whether the use of military force is appropriate. Given the propensity for armed conflicts to escalate and for mission creep to take hold, there is a real danger – exacerbated when confidence in the Commander in Chief’s judgment is low – that one man and a small coterie of advisers could ensnare the nation in prolonged, costly, and internationally destructive conflicts.

Moreover, vesting such decisions solely in the executive branch creates a perverse incentive for members of Congress to sit silently on the sidelines and avoid weighing in on such decisions until it is clear in which direction the political winds are blowing. Such gamesmanship, which might serve the short-term interests of politicians, deprives the People of critical representation on what can be one of the most dire issues of the day.

On the other hand, there are sound reasons to think the executive branch is often better situated to make such decisions. Despite the virtues of public debate, it can be unwise for a nation to advertise its military intentions to potential adversaries, and when the use of immediate force is necessary, the president can act with greater decisiveness, secrecy, and speed than the Congress. Moreover, the world is different today than at the time of the founding, and exigencies like terrorism and the risk of nuclear attack could sensibly require immediate action and even preemptive strikes.

The plain and simple fact is that there are reasonable arguments for dividing power in different ways. But there is no reasonable argument for allowing the president simply to assume this power through sheer force of will and self-interest. What should be the proper role for the president and for the Congress in authorizing the use of military force? Our nation is long overdue for a full, free, and earnest debate on this question. It is high time we have one.