As North Korea has moved closer to possessing nuclear-armed missiles that can strike the United States, President Trump raised fears of nuclear conflict this week by promising that North Korea could face “fire and fury like the world has never seen” if it “make[s] any more threats to the United States.”

While many have criticized the substance of Trump’s statement, nearly all journalistic commentary I have seen (for example, here and here, but see this story) has nevertheless assumed that because the President possesses the “nuclear codes” he in fact has authority, if he chooses, to bring the promised “fire and fury” on North Korea.  As a matter of constitutional law, that assumption is simply false.

 The Constitution divides authority over the military between the President and Congress. While the President is “Commander in Chief” of the Armed Forces under Article II of the Constitution, Congress holds the power to “declare War.”  Congress also holds sole authority to raise and support armies and navies in the first place and to establish rules and regulations governing them.

 How exactly these authorities fit together—the President’s Commander-in-Chief power on the one hand and Congress’s authority to raise armies and declare war on the other—is admittedly a matter of some dispute.  For reasons I explain in this paper, Congress’s authority over military resources entails power to impose almost any conditions or limitations it likes on use of those resources—and Congress might consider exercising that authority in the next round of annual appropriations legislation this fall.  Even without such explicit limitations, however, most scholars think Congress’s power to declare war means that Congress must authorize any significant offensive military operation.  (For discussion of the various schools of thought, see this Just Security post a few months ago by Marty Lederman; for scholarship on the original understanding, see this one by Andrew Kent on Lawfare.)

In practice, of course, the executive branch has undertaken numerous past military operations without advance congressional approval.  But even the executive branch has identified limits to this authority.

In a series of opinions across administrations (for example, here, here, here, and here), the Justice Department’s Office of Legal Counsel has taken the position that Presidents may take military action on their own authority to protect American lives and property and other important national interests. At the same time, however, the Office has indicated in key opinions that any such operation must generally be “limited in nature, scope, and duration.”  In the Office’s view (as expressed in a 2009 opinion), a “prolonged and substantial military engagement[],” particularly one “involving exposure of U.S. military personnel to significant risk over a substantial period,” would constitute a “war” within the meaning of the Declare War clause, even if more limited military operations do not. Accordingly, any such operation requires advance congressional authorization and cannot be undertaken on sole presidential authority.

 During the Obama Administration, the Office employed this framework to approve a limited planned campaign of airstrikes against the Libyan government.  Earlier, the Office employed similar reasoning to approve interventions in Haiti (2004), Bosnia (1995), and Somalia (1992).  The Office took a broader view of Presidential war power in a 2002 opinion regarding the Iraq War, but the President did not act on this view—President Bush instead obtained congressional authorization.  (By way of disclosure, I should say that I worked as an Attorney Adviser at OLC between 2009 and 2012, at the time when the Office issued the Libya opinion, but I am obviously speaking here only for myself and not necessarily representing the Office’s views.)

Some commentators dislike OLC’s “nature, scope, and duration” standard. After all, this framework does give the executive branch considerable leeway to undertake military operations without seeking congressional approval.

 Whatever else may be said about it, though, framework accounts fairly well for historical practice.  Although some Presidents (most recently George W. Bush, as reflected in the 2002 OLC opinion) have asserted broader theories of Commander-in-Chief power, presidents have rarely acted on such views.  For example, Presidents George H.W. Bush and George W. Bush claimed constitutional authority to undertake the Gulf and Iraq Wars, respectively, without congressional approval.  Yet in both cases they in fact obtained authorization from Congress.

The post-September 11 Authorization for Use of Military Force authorized the war in Afghanistan. The same authorization at least arguably authorized the current campaign against ISIS, and Congress at least arguably authorized the Vietnam War in the Gulf of Tonkin Resolution. Before that, the two World Wars were formally declared by Congress.  In contrast, many other military strikes and operations, up to and including the campaign in Libya, have been conducted on sole presidential authority, but these uses of force have generally been more limited in scope.

 The main outlier to this pattern is the Korean War—a massive conflict that Congress never formally authorized.  This example, however, seems out of step with the broader pattern of historic practice, and the more recent OLC opinions implicitly repudiate it.  What’s more, the Korean War (like the Libya intervention and some others) was fought to enforce a United Nations Security Council resolution, a factor that may not be present in other conflicts.

How, then, does all this relate to the current controversy over Korea?

To begin with, insofar as the President holds constitutional authority to defend American lives and property, he might well hold authority as Commander in Chief to take military action to forestall an immediate risk to American lives, such as an imminent missile launch.  That theory, at least, seems necessary to explain the President’s authority over the nuclear launch codes in the first place.

Yet outside of any such scenario—that is, if North Korea continues to make generalized “threats” but does not present an immediate, objectively ascertainable risk to Americans—it is hard to see how a military strike against North Korea would not amount to launching a “war” in the sense requiring advance congressional approval, even under the executive branch’s own broadly permissive recent opinions.

 While I am no expert on this point, most analysts appear to believe that any limited military strike by the United States could trigger rapid escalation of the conflict. In all likelihood, North Korea would respond with a massive conventional or nuclear attack on South Korea, other U.S. allies such as Japan, and U.S. forces in the region.  To be effective, then, an initial U.S. strike would itself need to be massive:  it would need to obliterate the North Korean missiles, artillery, and other forces that could be deployed against us and our allies. 

Either way, the end result would not be a limited operation, but rather a massive conflict causing thousands or possibly millions of deaths.  That is not the sort of military engagement the Constitution allows the President to undertake on his own authority.

 Seeking congressional approval in these circumstances would carry significant strategic drawbacks.  Uncertainty is sometimes essential to deterrence, and congressional legislation either expanding or limiting the President’s options might only complicate diplomatic efforts to resolve the conflict.  But these concerns don’t provide a reason to disregard the Constitution. The Constitution limits use of military force on sole presidential authority, and even under the executive branch’s own permissive understanding of this power, launching a war against North Korea would overstep those limits.

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