Donald Trump's withdrawal of troops from Syria is a huge win for Damascus, Moscow and Tehran

US President Donald Trump yesterday stunned Washington by ordering the complete withdrawal of all US forces in Syria, beginning immediately.

Perhaps we shouldn’t be surprised. Mr Trump frequently promised a withdrawal and tried to order it several times, only to be blocked by a near-unanimous outcry.

Most other parties can see that this move makes no sense, especially since it is predicated on the delusion that ISIS is no longer a meaningful threat.

That is obviously wrong. It is a reprise of George W Bush announcing in 2003 that it was game over in Iraq, with a “mission accomplished” banner as a backdrop – a speech that was followed by a sharp rise in insurgency and attacks.

Estimates suggest about 20,000 ISIS militants remain active in Syria and Iraq and no one really believes the group has been decisively "defeated”.

Although this rapid withdrawal has a certain nativist and neo-isolationist appeal for Mr Trump, it completely sabotages two of his key international priorities.

Along with challenging China and others on trade, Mr Trump has identified combating terrorism and confronting Iran as his main foreign policy goals.

Walking away from Syria, especially for no good reason and at an extremely precarious time, when the post-ISIS environment is being shaped daily on the ground, drops the ball decisively on both.

Areas where the ISIS caliphate used to predominate and that US-backed forces now control will likely fall into the hands of the Assad regime, Iran or Hezbollah if US troops abandoned the field.

That's a huge win for Damascus, Moscow and Tehran. It would be entirely possible for Iran to conclude that the financial cost of the new sanctions is more than compensated by this titanic strategic victory.

It might even make a Tehran-controlled land bridge from the Iranian border through Iraq and Syria into Lebanon, and all the way to the Mediterranean sea, at last a reality. Tehran could be forgiven for concluding its earlier sacrifices were worth every penny.

In the process, of course, ISIS is likely to make a comeback, presenting itself as the only effective defender of local Sunni Arab populations being set upon by fanatical sectarian enemies. It's probably the only scenario that could lead to a quick and comprehensive resurrection of the extremist group.

Worse, this is exactly what happened in Iraq when Barack Obama continued to withdraw US forces precipitously until 2011, causing a previously moribund Al Qaeda in Mesopotamia to morph into ISIS and launch its rampage.

The withdrawal would not only be a huge victory for Tehran, its proxies, and ISIS. It will also deliver a death blow to US credibility, given the abandonment of Kurdish and Arab groups in the Syrian Democratic Forces, which formed Washington's ground troops fighting ISIS and will now be thrown to the mercy of Turkey and the Syrian regime.

ISIS is not fully defeated and yet those who fought and sacrificed their lives in battling the extremists are about to be callously abandoned. If that happens, why anyone would ever again regard Washington as a faithful and reliable ally?

There is no logical or strategic justification for this reckless move. Hence almost all of Mr Trump's key officials, including national security adviser John Bolton, Secretary of State Mike Pompeo, special envoy to Syria Jim Jeffrey and head of the anti-ISIS coalition Brett McGurk have all publicly insisted the US was in no way preparing to leave Syria.

Mr Trump knows he has virtually no support for this among his own cabinet or Republicans in Congress but is moving quickly to make it a fait accompli before he can be stopped. It is reminiscent of how, when his former economic adviser Gary Cohn asked him why he clings to ridiculous views on trade, he answered: "I just do".

But he must be persuaded to reverse this disastrous error. It is fortunate, in this case at least, that Mr Trump is so mercurial and changes his mind frequently in often dramatic ways.

This is the same man who went from threatening North Korea with "fire and fury" to rhapsodising about having "fallen in love" with its despotic leader Kim Jong-un a few months later.

On the same day he had announced a withdrawal from Syria, there was a very useful example of his ability to make a volte face on an issue he had strongly campaigned on.

For weeks, Mr Trump insisted he needed $5 billion for a border wall between the US and Mexico, insisted he would not take a penny less and vowed to shut down the government if he didn't get it.

But yesterday, the Senate announced a new agreement for government funding until February, which includes no money for the wall and postpones the next round of negotiations until the new year, when Democrats will control the House of Representatives.

Mr Trump continues to bluster, rage and promise that his wall will be built, with or without Congress's help. But the border wall remains entirely his fantasy while the government has remained open, despite his declarations.

In short, Mr Trump is perfectly capable of conceding that he has no intention of following through on any given pronouncement and that, on second thoughts, some flawed policy – whether shutting down the government or charging out of Syria – won’t be happening.

Those around Mr Trump still have a chance to persuade him to avoid this catastrophic blunder. Washington’s Arab allies should do whatever they can to help. It's imperative they succeed – for Arab and American interests alike.

Hussein Ibish is a senior resident scholar at the Arab Gulf States ­Institute in Washington