THE spectacle of American-trained Iraqi Army troops dropping their weapons and fleeing in the face of an offensive by the radical Sunni ISIS militia evokes memories of the collapse of South Vietnam's American-trained military in 1975. In both cases, weak, nominally democratic but corrupt and factionalised American-built states discovered, after the departure of their American patron, that they could not count on large elements of their own military to fight. Deploying force to control territory is the most basic function of any state, and any government that cannot do so is through. Fox News finds an anonymous "US intelligence official" predicting a Saigon-like endgame: "Baghdad is going to be overrun. The Green Zone is going down." That would certainly be a major headache for the Obama administration; as in 1975, the collapse of a former American proxy state and the victory of America's bitter enemies would project an image of American weakness in both international and domestic politics. How much blood and treasure should America devote to preventing this from happening? In the paper this week, we argue that America should work to stop ISIS, specifically by arming and training the Iraqi army and moderate rebels in Syria. Those seem like pretty reasonable steps, though it's worth noting that the Iraqi soldiers who threw down their guns this week were already armed and trained by the US. But I have reservations about whether it would be a good idea for America to take a more aggressive role in fighting ISIS, or risk appearing to take the lead in that conflict. To get one threat scenario out of the way: Baghdad going the way of Saigon is wildly unlikely. ISIS has perhaps 11,000 fighters to the Iraqi Army's 250,000. The Iraqi troops who deserted in Mosul and Tikrit were mainly Sunnis, resentful of discrimination by the largely Shiite government of Nuri al-Maliki. The army's Shiite soldiers are more likely to fight for the government, and would certainly fight to protect Baghdad from ISIS's fanatics, who consider Shiites infidels and have carried out mass executions. More important, Iran will intervene to stop ISIS from taking Baghdad, or from overthrowing the Iraqi government, which is increasingly aligned with Tehran. Iran has already reportedly deployed two battalions of its elite, battle-hardened Revolutionary Guard to take back territory from ISIS inside Iraq. The Kurdish peshmerga, too, are entirely capable of keeping ISIS out of Kurdistan. The risk to America is not that ISIS overruns the Green Zone, but that Iraq reverts to the Sunni-Shiite civil war that raged during most of the American occupation, and that this time the government is pushed towards an explicit alliance with Iran while the Sunni tribes shift to an alliance with ISIS. Ultimately, ISIS might successfully carve out a pseudo-state stretching across parts of Syria and Iraq, like those operated by Hezbollah in southern Lebanon, Hamas in Gaza, the Taliban in regions of Afghanistan and Pakistan, and the Kurds in northern Iraq.

For the past few years, the Obama administration has consistently tried to disentangle American foreign policy from infernal situations such as this one. Barack Obama made that policy explicit in his speech at West Point in May, as well as in a recent conversation with reporters on board Air Force One, in which he earthily described the kernel of his approach to foreign policy as "don't do stupid [stuff]". After five years of trying, Mr Obama may have thought he was finally out of Iraq, but the heat of the ISIS offensive threatens to pull him back in. Mr Obama has promised unspecified help to the Iraqi government. America initially rejected appeals from Mr al-Maliki to carry out air strikes against ISIS; that is now reportedly being reconsidered. The question is whether the deteriorating situation in Syria and Iraq will throw a big wrench into Mr Obama's programme of turning American foreign policy away from the endless bloody internecine warfare of the Middle East, and towards more promising subjects such as trade, East Asia, and the international legal order.

In the end, the wrench in question will probably be small. In terms of domestic politics, Republicans today are split between a traditional (though increasingly risk-averse) hawkish camp and a rising libertarian anti-interventionist one. (The hawks are further confused by the fact that fighting ISIS would mean fighting alongside their nemesis Iran, to protect the Iran-backed Iraqi government.) Republicans will criticise Mr Obama's Iraq policy, but as with Libya and Syria, the critique will be incoherent and will not demand any concrete policy change (something Lexington criticises here). Democrats, meanwhile, once hoped to boast of a positive Middle East foreign-policy agenda oriented towards supporting new Arab democracies and reaching a peace settlement between Israel and Palestine. But with that scenario having gone down in flames over the past year or two, there's no real Democratic angle on Syria or Iraq, one way or the other.

In terms of international strategy, large-scale intervention against ISIS has a lot of downsides for America. There can be no justifying such an intervention on the grounds that it would lead to a sustainable, autonomous, democratic Iraq. The United States lacks the capacity to build such an Iraqi state, or to resolve Sunni-Shiite sectarian warfare. This was decisively proven in a large-scale longitudinal experiment, funded by the Defence Department, that began in 2003, ran for eight years and cost over a trillion dollars. Given the Iraqi government we have, the question is whether to commit major resources to propping it up, a task which Iran will no doubt carry out anyway. America could still play a bidding war against Iran for influence within Mr al-Maliki's corrupt, Shiite-dominated state, offering military and other goodies; but that would cost money, exacerbate corruption, and implicate America in the Iraqi regime's discrimination against its Sunni citizens. Iran would ultimately win the struggle for influence anyway, and it's hard to see what would be achieved.

The option of modestly increasing military support for Iraq against ISIS seems safer. It shows ISIS that its aggression is not entirely cost-free, and it broadens the international coalition backing the Iraqi government. This may forestall the impression that Iraq has simply descended into a regional war between Sunni Islamicist jihadist proxies on the one hand, and Shiite Iranian jihadist proxies on the other. It is much easier and less risky for America to aid the Iraqi government as part of an anti-ISIS coalition with Turkey and Iran than to do so in the guise of Iraq's leading patron or ISIS's archenemy. And a limited programme of military aid might be enough to ward off Republican attacks that the administration is doing nothing about ISIS; critics will be hard pressed to explain to a war-weary public why America should be doing even more to reinsert itself into Sunni-Shiite bloodshed in Iraq. This, in fact, appears to be the policy the Obama administration has selected.

Whatever policy emerges on dealing with ISIS, it's clear that America's long-term strategy for the Middle East has to be oriented towards letting local powers settle the geopolitical balance themselves. Iran, Turkey, and other regional players will have to take the lead in backing the Iraqi government and combating ISIS, because America lacks the expertise, the political will, and ultimately the capacity to do that job. We've tried it; it didn't work. Perhaps the endgame will end up looking something like what happened in South-East Asia 40 years ago. After America's departure and the collapse of its hapless proxies, regional powers moved in to assert their interests and create a new geopolitical order. America continued to protect clearly pro-American, reasonably stable capitalist states such as Thailand and the Philippines. Vietnam intervened to clean up the mess made by its insane neighbour in Cambodia, while drawing the line against its troublesome frenemy China with a brief border war. A few decades later, this new order had become stable enough that several of the countries America spent the early 1970s bombing had evolved into friends and trading partners. It's probably wildly optimistic to hope that the Middle East could have that future, and the situation could still get a lot worse. But Iran and Turkey have much more ability than America to shape this destiny, for better or worse.

Dig deeper:

Lexington on Barack Obama's cautious, hyper-realistic approach to Iraq