President Donald Trump speaks on North Korea. (Jonathan Ernst/Reuters)

Yesterday, President Trump warned that “North Korea best not make any more threats to the United States,”  or else “[t]hey will be met with fire and fury like the world has never seen.” This certainly sounds like a threat to launch an attack against North Korea. If so, it is important to ask whether any such action requires congressional authorization, or whether Trump has the power to do it on his own. The answer is that the Constitution does indeed require congressional authorization for a large-scale attack on North Korea.  But Trump might be able to get away with launching an unauthorized attack  anyway.

I. Why the Constitution Requires Congressional Authorization.

The Constitution  very clearly reserves to Congress the power to start a war. The Founders did not want any single man to be able to take the nation to war on his own. Even Alexander Hamilton — the strongest supporter of sweeping presidential power among the framers  — understood that only “the Legislature have a right to make war” and that “it is . . . the duty of the Executive to preserve Peace till war is declared.”

As the failures of President Obama’s Libya policy dramatically illustrate, obeying the constitutional requirement of congressional authorization is  more than a legal technicality. It also helps ensure that we do not initiate dubious conflicts at the behest of a single man, and that we maximize the chances of success if we do start a new war. If the president is required to get congressional authorization before starting a war, he is forced to build up a broad political consensus behind his decision, which in turn increases the likelihood of a beneficial outcome.

It is possible that the president has the power to initiate small-scale military actions that fall short of qualifying as “war,” even without congressional authorization. In my view, this could justify the very limited air strike Trump launched against Syria back in April, though some scholars disagree. Regardless, a conflict with North Korea is unlikely to be limited in this way. Secretary of Defense James Mattis – who, unlike Trump, tends to know what he’s talking about – has said that a conflict with North Korea “would lead to the end of its regime and destruction of its people” and that it “would be probably the worst kind of fighting in most people’s lifetimes.” That sure sounds like a war to me! I don’t think you have to be a lawyer or a constitutional law maven to recognize that a conflict that costs many thousands of lives and may well involve the use of nuclear weapons qualifies as “war” by any reasonable standard.

Trump would not need congressional authorization if North Korea strikes first, or if it is about to do so. In that event, Trump would not be initiating war, but merely  waging one already begun by the enemy. But so far, at least, it does not seem as if North Korea is about to attack.

North Korea may be a special case because the Korean War of 1950-53 never fully ended. Technically, the July 1953 ceasefire is an armistice, not a full-fledged peace treaty. North Korea has even at times stated that it no longer considers the armistice valid. This could open the door for the Trump administration to argue that an attack on North Korea would not be the start of a new war, but merely a continuation of an ongoing conflict that never ended. Still, there has not in fact been large-scale fighting between the US and North Korea since 1953, and most experts would agree that a massive attack of the sort envisioned by Trump would indeed be the start of a new war. Moreover, because Congress never authorized the original Korean War (which was, dubiously declared a mere United Nations “police action”), there is no ongoing authorization for military action as far as the US Constitution is concerned.

II. Why Trump Might be able to get Away with an Unauthorized Attack.

Unfortunately, Trump might be able to start a war even without congressional authorization, regardless of what the Constitution requires. This is an area where adherence to the rule of law depends mainly on political norms. The courts are highly unlikely to intervene. With notable exceptions, such as the Korean War, presidents have generally sought advance congressional authorization for large-scale military actions comparable to the one now under discussion. That is what happened in the cases of the Vietnam War, the post-9/11 invasion of Afghanistan, and both Iraq wars. Unilateral presidential military actions typically involved situations where the enemy attacked or declared war first (as in the 1989 Panama intervention) or cases where the expected military action was brief and on a very small scale, involving little or no combat (as in the case of President Clinton’s 1994 intervention in Haiti, among many other examples).

Unfortunately, this norm has frayed in recent years, in considerable part because President Obama initiated two large-scale wars without congressional authorization – his 2011 intervention in Libya and the still-ongoing war against ISIS. In January, I  warned that these  precedents were a dangerous “loaded gun” that  Obama left to Trump, and urged Congress to reassert its war powers.  Whether it will actually do so remains unclear.

Earlier today, Alaska GOP Senator Dan Sullivan – whose state might be in the line of North Korean fire in the event of war – said that he believes that a preemptive attack does indeed require congressional authorization. A few principled members of Congress, such as Democrat Tim Kaine and Republicans Rand Paul and Justin Amash, have consistently insisted on the need to prevent presidents from initiating war on their own. But many others have either ignored the issue or succumbed to partisan bias – complaining about unauthorized warmaking when it is initiated by presidents of the opposing party, but backing it when it is their own man who does it.  For this reason, among others, it is difficult to say whether Congress will actually assert itself in this case or not. Whether or not it does so may depend on a variety of political factors, such as Trump’s record unpopularity, and whether GOP congressional leaders believe that a war is likely to lead to a disaster that might be blamed on their party.

To avoid misunderstanding, I should emphasize that I agree that North Korea is a dangerous menace and I would be happy to see this brutal communist regime – a real-life 1984 that is probably  the most oppressive in the world – overthrown. But it is still unwise to initiate a massive war without a broad political consensus favor and without first securing the support of key allies in the region, such as Japan and South Korea. At this point, they don’t seem eager for a conflict. Such caution is even more important in a situation where war could result in the use of nuclear weapons and enormous civilian casualties. As conservative defense policy expert Eliot Cohen explains, we are not well prepared for all-out war against North Korea, and Trump is a dubious choice to lead any such effort.

Of course, all of this may be irrelevant if Trump’s threat turns out to be just hollow bluster. North Korea has already, in a sense, called his bluff by threatening to attack Guam,  and there has been no indication that a US military response is imminent. This could be yet another case where Trump engage in impulsive grandstanding without carefully considering the implications.

If Trump does not make good on his threats, there will be no constitutional problem, and we  will avoid a massive war on the Korean peninsula – at least for now. But making hollow threats is not costless. Doing so may  erode the credibility of any future threats Trump might make. That in turn may increase the likelihood of conflict in the future.

UPDATE: Michael Ramsey comments on this post here, agreeing with much of it, but also arguing that Libya may not be a relevant precedent because it was not a “large-scale” war from the standpoint of the US and “the Obama administration expressly defended it on the grounds that it was small scale.” The Obama administration did indeed make that argument. But if a war that involves many weeks of bombing for the purpose of overthrowing the opposing nation’s government can qualify as “small scale,” then so can a wide range of conflicts, including an attack on North Korea intended to destroy its nuclear forces. At least initially, such an attack might not involve US ground forces, and would be waged for more limited objectives than the Libya intervention.

On the war against ISIS, Ramsey points out that the administration tried to justify it based on the 2001 AUMF. True. But that justification was extremely flimsy and similar reasoning to could be used to justify a wide range of future conflicts.