During the coming year, the United States, in occasional concert with Israel, must confront expanding terrorist threats. Topping pertinent concerns in Washington and Jerusalem will be an assortment of jihadi groups, some spawned by the al-Assad regime collapse in Syria and some by coinciding reconfigurations of Hamas, Hezbollah, Islamic Jihad, and Houthi criminals. Also predictable are (1) strengthened and dispersed Fatah units beyond Judea/Samaria (West Bank); and (2) variously lethal synergies between criminal terrorist organizations that include al-Qaeda and ISIS remnants.

Under the protective tutelage of an American president, “We the People” are entitled to expect basic safety in world politics. At a minimum, we should all be able to assume that wider and consistently capable circles of public authority remain poised to thwart terror attacks.

In terms of United States law, the authoritative roots of core security assurances go back to 17th century English philosopher Thomas Hobbes. Though likely unfamiliar to America’s current president and his senior defense advisors, Hobbes’ Leviathan was integral to the political thought of Thomas Jefferson. The erudite author of the Declaration was widely read by all categories of educated persons.

Regarding US counterterrorist preparation, America’s national security establishment must get ready for all contingencies, most plainly jihadi terrorists who seek “martyrdom.” This includes fashioning conceptual foundations for future Osama Bin-Laden “elimination-type” operations.

During the Obama years, one conspicuously major targeted killing of a jihadi terrorist was the September 2011 US drone-assassination of Anwar al-Awlaki in Yemen. That case was notably “special” in one generally overlooked or underestimated aspect: Jihadi al-Alwaki was born in New Mexico, and was therefore a US citizen. At the same time, despite the US Constitution’s Fifth Amendment protections regarding “due process,” it represented a tactical option that could sometime need to be repeated.

Here, a presumptively effective tactic would simultaneously undermine American law and justice.

What should be decided in Washington? Each and every trade-off option would be injurious. Even if we take with utmost seriousness Cicero’s reasonable injunction (“The safety of the people shall be the highest law”), it’s not clear which operational choices would best serve such indispensable “safety?”

What precise legal guidelines should Americans follow in these settings?

To respond properly, Trump and his designated counselors will need to inquire: “Is it sufficiently legal to target and kill jihadi terrorists if precise linkages between prospective targets and discernible attack intentions can be documented?”

To meaningfully answer this critical question, it will first be necessary for Trump’s national security officials to ask whether a proposed terrorist killing plan would be gainfully preemptive or just narrowly retributive. If the latter, a judgment wherein national self-defense was not in any way the underlying operational rationale, authoritative determinations of legality could become more problematic. It would not be sensible to launch risky defensive actions against terrorist adversaries solely because these actions could meet jurisprudential standards.

 It gets even more complicated.

Assassination is explicitly prohibited by US law. (See Exec. Order No. 12333, 3 C.F.R. 200 (1988), reprinted in 50 U.S.C.  Sec. 401 (1988)). Generally, it is also a crime under international law, which, though not widely understood, is part of American domestic law.

Still, at least in certain more-or-less residual circumstances, the targeted killing of jihadi terrorist leaders could be correctly excluded from ordinarily prohibited behaviors. Accordingly, such peremptorily protective actions could still be defended as permissible expressions of national law-enforcement.

A similar defense could sometimes be applied to the considered killing of terrorist “rank-and-file,” especially where such selective lethality had become part of an already-ongoing pattern of US counter-terrorism. Earlier, for example, the United States widened the scope of its permissible terrorist targeting in parts of Iraq, Afghanistan, and Syria. This widened arc of permissibility — one which now modifies more stringent rules of engagement concerning human target identification — represented a byproduct of continuously developing drone technologies.

In the best of all possible worlds, there would be no need for any decentralized or “vigilante” expressions of international justice. Obviously, we don’t yet live in such an ideal world. Instead, enduring uneasily in an historically anarchic world order- – a context that international law professors prefer to call “Westphalian.”

At some still-indeterminable point, terrorist escalations could lead to instances of chemical, biological or nuclear attack. These unprecedented attacks (ones that are sui generis in law) might be undertaken by assorted sub-state adversaries or by certain “hybrid” combinations of state and sub-state foes. Ironically, in the policies of US ally Israel, dominant concerns have centered on Iran-Hezbollah and Iran/Hamas combinations. Here, an evident irony stems from the fact that one Iranian surrogate (Hezbollah) is Shiite while the other (Hamas) is Sunni.

In our persistently anarchic and prospectively chaotic world legal system, assorted jihadi leaders are already responsible for the mass killing of noncombatant men, women, and children of many different nationalities. It follows that wherever such leaders are not suitably “terminated” by the United States or Israel in the tumultuous Middle East, egregious terror crimes will almost certainly continue and be left unpunished.

Any impunity would be inconsistent with the universal legal obligation to punish international crimes, a jus cogens or peremptory obligation reaffirmed at the original Nuremberg Tribunal and in the subsequent Nuremberg Principles.

Inevitably, complex considerations of law and tactics will intersect and inter-penetrate. In this connection, the glaring indiscriminacy of most jihadist operations is rarely if ever the result of adversarial inadvertence. Typically, it is the intentional outcome of violent terrorist inclinations, unambiguously murderous ideals that lay embedded in the jihadist terrorist leader’s operative views of insurgency.

For jihadists, there can never be meaningful distinctions between civilians and non-civilians, between innocents and non-innocents. For these active or latent terrorist murderers, all that really matters are unassailably immutable distinctions between Muslims, “apostates” and “unbelievers.”

As for the apostates and unbelievers, it’s quite simple. Their lives, believe the jihadists, have no value. Prima facie, they have no immunizing sanctity. In law, both international and national, every government has the right and obligation to protect its citizens against external harms.

Usually, assassination is a certifiable crime under international law. Yet, in our essentially decentralized system of world law, extraordinary self-help by individual states is often necessary, and more-then-occasionally the only real alternative to passively sufferance of terror crimes. In the absence of particular targeted killings, terrorists would continue to create havoc against defenseless civilians almost anywhere of their choosing and with unjust impunity.

A basic difficulty is that jihadi terror criminals are usually immune to the more orthodox legal expectations of extradition and prosecution (aut dedere, aut judicare). This is not to suggest that the targeted killing of terrorists will always “work” — there is literally nothing to support the logic of any such suggestion — but only that disallowing such killing ex ante might not be operationally gainful or legally just.

If carried out with aptly due regard for pertinent “rules,” targeting terrorist leaders could remain consistent with the ancient legal principle of Nullum crimen sine poena, “No crime without a punishment.” Earlier, this original principle of justice had been cited as a dominant rationale for both the Tokyo and Nuremberg war crime tribunals. Subsequently, it was incorporated into customary international law, an authoritative source of law identified inter alia at Article 38 of the Statute of the International Court of Justice.

 By both the codified and customary standards of contemporary international law, all terrorists are hostes humani generis, or “common enemies of humankind.” Still, choosing precisely which terrorists ought to be targeted remains a largely ideological rather than jurisprudential matter.

Overall, in his consideration of assassination or targeted-killing as counter-terrorism, President Trump should consider the clarifying position of 18th century Swiss scholar Emmerich de Vattel in his most famous work, The Law of Nations, or the Principles of Natural Law (1758): “The safest plan is to prevent evil where that is possible. A Nation has the right to resist the injury another seeks to inflict upon it, and to use force and every other just means of resistance against the aggressor.”

Even earlier, the right of self-defense by forestalling an attack had been asserted by the foundational Dutch scholar, Hugo Grotius, in Book II of The Law of War and Peace (1625). Recognizing the need for what later jurisprudence would reference as threatening international behavior that is “imminent in point of time,” Grotius indicated that self-defense must be permitted not only after an attack has already been suffered, but also in advance, where “the deed may be anticipated.”

Further on, in the same chapter, Grotius summarized: “It be lawful to kill him who is preparing to kill.” Interestingly, Vattel, Pufendorf and Grotius were all taken into primary account by Thomas Jefferson in the American Declaration of Independence.

International law is not a suicide pact. “Where the ordinary remedy fails, recourse must be had to an extraordinary one.”

Donald Trump is obligated to comply with the rules and procedures of humanitarian international law, yet he must also bear in mind that jihadist enemies will remain unaffected by these or any other jurisprudential expectations. Assassination and broader forms of preemption may sometimes be not only allowable under binding international law, but indispensable.

Conversely, there are occasions when strategies of assassination could be determinedly legal but be operationally ineffectual. Recalling the close connections between international law and US law — connections that extend to direct and literal forms of “incorporation” – -an American president can never choose to dismiss the law of war on grounds that it is “merely international.”Always, President Trump should consider decipherable connections between targeted killings, counter-terrorism, and United States Constitutional Law.

Under US law, we are bound to inquire, should an American president ever be authorized to order the extra-judicial killing of a United States citizen — even one deemed an “enemy combatant” — without meaningful reference to “due process of law?” On its face, any affirmative response to this query would be difficult to defend under the US Constitution.

Operational approval would need to be based upon a reasonably presumed high urgency of terror threat. Any such allegedly “authorized” targeted killing of US citizens would express potentially irremediable tension between indissoluble citizen rights and peremptory requirements of public safety. Going forward with obligatory counter terrorist preparations, the US president will need to keep this firmly in mind.

US policy on assassination or targeted killing will have to reflect a very delicate balance. Most important, in any such calculation, will be the protection of civilian populations from jihadist terror-inflicted harms. In those circumstances where harms would involve unconventional weapons of any sort — chemical, biological or nuclear — the legal propriety of targeting jihadists could be patently obvious (per Cicero, above) and “beyond reasonable doubt.”

In sum, for both the United States and Israel, legal assessments of targeted killing ought never be undertaken apart from correlative operational expectations. This means that before any “extraordinary remedies” should be applied, these measures would be not only legally correct, but tactically cost-effective. In the end, as we may finally be reminded by Cicero in The Laws, “The safety of the people shall be the highest law.”

Louis René Beres, Emeritus Professor of International Law at Purdue, is the author of many books and articles dealing with nuclear strategy and nuclear war, including Apocalypse: Nuclear Catastrophe in World Politics (University of Chicago Press, 1980) and Security or Armageddon: Israel’s Nuclear Strategy (D.C. Heath/Lexington, 1986). His twelfth book, Surviving Amid Chaos: Israel’s Nuclear Strategy, was published by Rowman and Littlefield in 2016. A version of this article was originally published by Jewish Business News.

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