BASHAR AL-ASSAD’S chemical attack on the town of Douma on April 7th has been widely condemned. But punishing Syria’s dictator is simpler than devising a coherent Syria policy. If Donald Trump orders a limited bombing campaign on Mr Assad’s palaces and military assets, it will not alter the course of the Syrian war. Thanks to his Iranian and Russian protectors, nothing now can realistically prevent Mr Assad from, in some sense, winning.

A retaliatory strike might at least change Mr Assad’s calculus about the use of chemicals as a way to terrorise the resistance. If he concluded, belatedly, that the price he will pay for using banned weapons again has become too high, Mr Trump would be justified in taking some credit. But, in other ways, Mr Trump is sowing confusion about America’s aims in Syria and threatening to undermine both its interests and those of its regional allies.

In a speech supposedly about infrastructure investment on March 29th, the president declared: “We’re knocking the hell out of ISIS. We’ll be coming out of Syria like very soon. Let the other people take care of it now.” On April 3rd Mr Trump said that having been “very successful against ISIS…it is time to come back home.”

At almost the same time, General Joseph Votel and Brett McGurk, America’s military commander in the region and the State Department’s envoy to the coalition against Islamic State (ISIS or IS), were delivering a very different message. Although the jihadists had been kicked out of most of the territory they once controlled in Syria, there were still pockets to be cleared, they said. General Votel warned that “the hard part is in front of us”. The tasks ahead, he said, are consolidation, stabilisation and reconstruction—the first two of which require a continuing military presence.

That presence currently comprises about 2,000 American troops in eastern Syria, largely engineers and special-operations soldiers, who are working and fighting alongside the Syrian Democratic Forces (SDF), a Kurdish-led group of militias. In the past year the SDF, with the help of American air power, has liberated most of the country’s eastern provinces from IS. The Americans and the SDF operate in an area east of the Euphrates. The river acts as an informal demarcation line between them and the Russian, Iranian and Syrian government forces, which control the territory to its west.

In January Rex Tillerson, then America’s secretary of state, made a far-ranging speech about the administration’s aims in Syria. Promising to not repeat Barack Obama’s mistakes in Iraq and Libya, Mr Tillerson said that America’s military commitment would be conditions-based rather than time-limited. American troops would stay in Syria long after the defeat of IS, both to ensure that it does not return and to keep Iranian and regime forces from entering the newly-liberated areas. He outlined five policy goals: preventing IS and al-Qaeda from re-emerging in Syria; supporting the UN-led peace process; countering the influence of Iran; helping to bring about the safe repatriation of Syrian refugees; and clearing the country of weapons of mass destruction. As a statement of intent, it was far removed from Mr Trump’s campaign commitment to destroy IS quickly and then get out. Mr Tillerson won praise from traditional foreign-policy experts, but there was scepticism too. In congressional testimony, Robert Ford, America’s last ambassador to Syria and a bitter critic of Mr Obama’s failure to arm moderate rebels before they were displaced by more extreme groups, described Mr Tillerson’s goals as admirable but mostly unachievable, given the resources available and the reality on the ground. Groups affiliated with al-Qaeda are in the north-west of the country, far from American forces, said Mr Ford. The UN peace process has faded into irrelevance, he added. Moreover, the American force in the east will have little impact on Iran’s clout in the west; most refugees want to return to territory held by the regime; and Mr Assad has shown little interest in giving up his chemical weapons, with Russia and China blocking UN efforts to compel him. Yet that does not mean the American mission in the east should be aborted, as Mr Trump would probably like. For a start, there would be a serious risk of IS re-emerging before local forces could deal with it unaided. Even if IS did not make a comeback, with the Americans gone, regime forces and Iranian-backed militias would soon be pushing across the Euphrates in an attempt to retake territory.

An emboldened Iran (and Russia) would undoubtedly see an American withdrawal from Syria as the likely prelude to pulling out of Iraq and perhaps the wider Middle East. Turkey would step up its assault on America’s Syrian Kurdish allies in the north. The relative safety that American forces have brought to some Syrians would evaporate. Finally, what little leverage America has recently bought in the process to determine Syria’s future would have been lost.

America’s allies in the region, particularly Israel and Saudi Arabia, want it not only to stay but to beef up its presence. Mr Tillerson’s successor as secretary of state, Mike Pompeo, and Mr Trump’s new national-security adviser, John Bolton, want to confront Iran, not concede the field to it. James Mattis, the defence secretary, is committed to finishing the job his troops started in Syria. They could yet convince Mr Trump. But the president’s tendency is to heed what his gut tells him his political base wants. If that is withdrawing quickly, as he promised on the campaign trail, then that is what is most likely to happen.