From the beginning, the argument that US President Donald Trump is somehow “good for Israel” has been foolish and incorrect.Now, with the president’s explicit promise to stop targeting Syrian President Bashar Assad – a gesture designed to impress his public that America’s overriding objective is still to eliminate Sunni Islamic State – Jerusalem can expect reciprocally greater hazards from Hezbollah.This expanding Shi’ite militia is, after all, a well-armed frontline surrogate of Syria, Iran and (ultimately) Russia.ISIS is no friend of Israel. Nonetheless, at the most crucial strategic level, it is far less threatening than Syria and Hezbollah. It follows that any newly-announced US policy that will strengthen Damascus and its proxies in order to diminish ISIS is fundamentally backward. At a minimum, it is fully contrary to Jerusalem’s survival needs.This visceral US policy is starkly injurious for Israel. It also undermines America’s own basic international legal obligations concerning the prevention and punishment of genocide. More specifically, the US, as a key party to the Genocide Convention, is doctrinally obligated to take suitably remedial actions against any genocidal regime. To be sure, this cornerstone human rights treaty would never allow a principal state party to openly join sides with an expressly active genocider.As for those who might respond to such an indisputable American jurisprudential obligation by suggesting otherwise, that is, that we simply ought not worry about international law, they should be reminded that the law of nations is an integral part of US law. This is the case, inter alia, by virtue of Article 6 of the US Constitution (the “Supremacy Clause”), and also because of assorted US Supreme Court decisions, especially the Paquete Habana (1900), and Tel-Oren vs. Libyan Arab Republic (1984). For Trump, chest-thumping rhetoric notwithstanding, the prospective implications of any US policy for Israel have never been examined very closely. To wit, in his vaunted campaign speech on Israel that was delivered on August 15, 2016, then candidate Trump called the Jewish state “America’s greatest ally,” but his subsequent proposals for actually dealing with the Middle East suggested something quite different. By agreeing to side with any nation that would join us in the fight against ISIS, it had already been made perfectly clear that Trump is perfectly willing to strengthen Syria, Iran and Hezbollah.Could this patently irrational posture have made any real sense for the US, let alone for Israel? In essence, one ought now to inquire, could it possibly have been consistent with peremptory American obligations under national and international law? Further, is President Trump’s conspicuous indifference to Syria’s continuing mass murder of civilians what an American president should be actively advancing as US national policy? Further, it is more than just a bit ironic that Israel, a state literally constructed upon the ashes of its own murdered people, should ever be encouraged to go along with such grotesquely barbarous presidential calculations.America now faces a bewilderingly complex and multi-vector civilizational war that will first have to be won at the intellectual or analytic level; that is, before it can ever be “won” on any more literal battlefield.The ancient Greeks and Macedonians had always spoken insightfully of war as a cerebral struggle of “mind over mind,” rather than “mind over matter.” Accordingly, before the US can be genuinely helpful to itself, and, as corollary, to its “greatest ally,” President Trump will first have to refrain from any further substitutions of commercial marketing strategy for authentically necessary geopolitical thought.There is more. Trump also needs to understand that the newly-explicit doctrine concerning his support for a genocidal regime in Damascus will simultaneously strengthen the hard-liners in Iran. Should the main hard-line group known as the Popular Front of Islamic Revolutionary Forces manage to identify a viable candidate to defeat Iranian President Hassan Rouhani in the May 19 election, this could make it considerably more likely that Iran will unhesitatingly “go nuclear.” One potential candidate set to oppose Rouhani is Mohsen Rezaei, a former chief of the Revolutionary Guard, who routinely associates the Rouhani administration with “senile diplomacy.”Does President Trump really want to enhance Rezaei’s chances to defeat the less menacing Rouhani? If he doesn’t, he ought not to continue with his gratuitously empty threats to put the Islamic Republic “on notice.” Soon, he must also factor into his required recalculations that an Iran more likely to go nuclear because of his increasingly sympathetic posture toward Syria would thereby incentivize Saudi Arabia to hasten any of its own plans for a reciprocal nuclearization. During my half-century of teaching international relations and international law at Princeton and Purdue, I typically reminded my students that there exist multiple and intersecting axes of conflict in world politics. Understood in terms of Trump’s largely incoherent foreign policy, this reminder now means we should not assume that inflicting preponderant harms upon any one particular enemy is necessarily in our overall best strategic interests, or in the best interests of a beleaguered ally such as Israel.Trump abhors complexity, especially in geo-strategic matters. In consequence, he remains so utterly focused on the single threat from ISIS that he is willing to tolerate ever-deepening military cooperation between Iran, Syria and Russia, and also eventual assertions of “countervailing” power from certain Sunni Arab states. From the particular standpoint of Israeli national security, any further encouragement of such tolerance could make it increasingly difficult or operationally impossible to consider residually defensive preemptions against Iran.Prime Minister Benjamin Netanyahu should promptly recognize, from the openly expressed standpoint of Trump’s inverted foreign policy preferences, that it would be reasonable to sacrifice Israel’s most indispensable security requirements for the (presumed) sake of defeating a single sub-state jihadist foe.ISIS does not present an existential threat to the United States, or to Israel. But by mistakenly focusing on the destruction of ISIS as if it were somehow a genuinely overriding security objective, Syria, Iran and Russia will be incrementally strengthened. Plausibly, the cumulative net effect of all such presidentially mishandled national priorities will be an unexpectedly virulent “Cold War II,” and a correspondingly diminished security position for both Washington and Jerusalem.President Trump ought not to become the most willing and law-violating servitor of the genocidal regime in Damascus. From the interrelated standpoints of the US and Israel, to decide otherwise would render both states (1) complicit in the very worst ongoing crimes against humanity, and (2) decreasingly able to provide basic security for their respective populations. It follows that the corrosive liabilities of his newly sympathetic posture toward Damascus would be both jurisprudential and strategic.The writer and is the author of many books and articles dealing with nuclear strategy and nuclear war.