President Trump (Pablo Martinez Monsivais/Associated Press)

Robert Malley served as special assistant and senior adviser to President Obama and White House coordinator for the Middle East, North Africa and the Gulf region. 

For clues as to how the Trump administration would like to deal with the Middle East, one need not look too far. As a candidate, and then as president, Donald Trump laid out three overarching principles that, one suspects, his national security team is busy trying to stitch together: to quickly defeat the Islamic State; to aggressively push back against Iran, imposing a steep price for its hostile activities; and to put “America first” — a concept that, applied to U.S. policy in the region, translates roughly into avoidance of costly, open-ended military entanglements. The principles are clear, understandable and irreconcilable: The administration could have one, or even two of the three, but not all of them at once. If it wants a robust approach to the Islamic State and an aggressive stance toward Iran, it will need to substantially ramp up U.S. military involvement. If it insists on keeping those numbers low and aspires to go after the Islamic State nonetheless, it will have to postpone the goal of decisively challenging Iran. And if it wants to confront Tehran while keeping the U.S. presence within bounds, the fight against the Islamic State inevitably will suffer.

Start with the admonition to steer clear of heavy U.S. military involvement, which, considering ill-fated precedent, may rank as one of Trump’s least objectionable pronouncements so far. Can the battle against the Islamic State proceed effectively within that constraint? Yes, and, indeed, it has. The United States has kept in check the numbers of its personnel on the ground (roughly 5,000 in Iraq, a few hundred in Syria), opting to work by, with and through the Iraqi government, which has the combat lead and provides the bulk of manpower, and to partner with various non-state actors in Syria. Progress against the Islamic State has been steady, if incremental, and efforts have been made to avoid decisions that might divert from that objective.

Add to this a far more confrontational stance toward Iran to, say, curb its role in Iraq or Syria, and the equilibrium will be upended. Administration officials make no secret of their desire to prioritize challenging Iran, pushing back on its military presence in Syria, impeding its activities or those of its allies in Iraq and interfering more aggressively with its arms shipments to those two theaters or to Yemen. But to do so under current circumstances would mean putting at risk U.S. troops and diplomatic personnel, many of whom live within striking distance of Shi’ite militia members that so far have been held back principally by Tehran. If it’s open season on Iran, two outcomes are likely. First, expect that restraining order to be lifted; that’s a reality that Defense Secretary Jim Mattis and national security adviser H.R. McMaster both experienced firsthand in the past. Second, expect Tehran to pressure Baghdad to either restrict the ability of U.S. forces to operate on its soil or, worse, ask that they depart. The former would cause considerable distraction from the fight against the Islamic State; the latter, were Baghdad to oblige, would render that fight all but impossible.

Alternative ways forward exist, of course, but they necessarily involve sacrificing one of the other two guidelines. First, the administration could choose to neutralize Tehran’s most effective deterrent — the ability to hinder and undermine the U.S. campaign against the Islamic State — by de-emphasizing that front, and accepting that, faced with diversion and disruption, progress against the Islamic State will need to slow down. Or the administration could decide to remove the tacit cap on its military involvement, opting to wage a two-front battle against the Islamic State and Iran. The addition of tens of thousands of U.S. troops could serve several purposes: Intimidate Iran; allow the United States to respond aggressively if intimidation were to fail; prosecute the war against the Islamic State in Iraq and Syria without regard to Iranian desiderata; and even pay less heed to the Iraqi government’s demands.

The Obama administration faced the same “trilemma,” and, by virtue of its actions, implicitly made its preference known. It combined a relatively modest military footprint with a focus on the Islamic State, because it felt that both the United States and the region could ill afford another Middle East quagmire, because it prioritized the fight against terrorism and because — while determined to check Iran’s hostile activities — it judged that there were other and smarter ways (tough but calibrated actions and sanctions, bilateral engagement and multilateral diplomacy, efforts to de-escalate tensions between Tehran and Riyadh, and the nuclear deal above all) to do so.

Trump considers the measures taken to contain Iran over the past few years to have been feeble, feels that Tehran has acquired disproportionate regional influence, has evinced scant regard for diplomacy or multilateralism and has made his distaste for the nuclear deal abundantly clear, so one might expect a different calculus. What is fanciful is an outcome that wishes away basic political and military constraints. In the business world, this rule went by the expression “Fast, Good or Cheap — Pick two.” There is no all-of-the-above option. Something will have to give.