After admitting I was foolish to have believed Trump was right to call Erdogan's bluff on the invasion, I find myself still thinking there may have been a rationale for Trump's move, as horrific as it has turned out to be.

Simon Tisdall describes a possible positive outcome from the negative reactions to Erdogan on the part of countries involved in the crisis:

https://www.theguardian.com/world/commentisfree/2019/oct/12/turkey-invas...

Erdoğan has managed the unthinkable: uniting all the other Middle East rivals
Simon Tisdall
Sat 12 Oct 2019

By invading northern Syria last week, Recep Tayyip Erdoğan achieved what many thought impossible – uniting all the regional countries and rival powers with a stake in the country in furious opposition to what they see as a reckless, destabilising move.

… Turkey’s relations with Europe were already at a low ebb because of its abysmal human rights record and thwarted EU membership bid. Now European leaders are paying a high price for past attempts to normalise Erdoğan’s authoritarianism. His latest actions prove he is no democrat, no ally and no friend.

While Europe has scant influence over what happens next, the US has plenty – but seems determined to throw it away. Despite denials, it is clear from the White House statement issued on 6 October that Donald Trump rashly agreed to Erdoğan’s invasion, without consulting his allies, and facilitated it by withdrawing ground forces.

… When Vladimir Putin sent forces to Syria in 2015, he put his money on Assad to win, but victory has proved elusive, while costs – political and financial – have mounted. Erdoğan’s move further complicates matters by obstructing the peace settlement Russia, Iran (and Turkey) have been pursuing via the so-called Astana process.

That’s why Russia is urging the Kurds, now the US has abandoned them, to agree a mutual defence pact or some kind of federal arrangement with Assad. And that’s why regime forces and pro-Iran militia are edging towards Kurdish-held areas from the south. Assad sees a chance to recapture lost territory. Erdoğan’s fatuous “safe zone” wheeze has no appeal for him.

Iran is not happy either, but for different reasons…

… After struggling to establish a pro-Tehran, Shia-dominated government in post-2003 Baghdad, Iran does not want to face another Sunni uprising across Syria and Iraq.

… Worries about an Isis revival, considered more likely thanks to Turkey’s move, are common to all the regional players. Strangely, in this respect at least, the US, Iran and Saudi Arabia, on the brink of war a few weeks ago, now find themselves on the same side.

Arab governments including Egypt, Jordan, Bahrain, Lebanon and the UAE, as well as the Saudis, have all condemned Turkey. After initially backing Syria’s rebels, several have pursued a cautious rapprochement with Assad in recent months, based on a shared interest in regional stability and upholding the principle of territorial sovereignty.

Arab leaders also object to Erdoğan’s support for the Muslim Brotherhood and his neo-Ottoman ideas about Turkish regional dominance. Like Russia and Iran, they calculate, reluctantly but pragmatically, that the only way to end Syria’s war, and contain Isis, is to back Assad. Erdoğan has now got in the way.

The crisis has produced another cautionary lesson: that American alliances cannot be trusted. The Kurds already knew this. They were betrayed in Iraq in 1991, when the US left Saddam Hussein in power at the end of the first Gulf war.

But US unreliability is new for the Saudi regime which, like Israel, ultimately depends on Washington for its security. The more the Saudis realise they cannot count on America, the more likely they are to mend fences with Iran. By some accounts, this is already happening.

How ironic if Trump’s Syrian cop-out – providing a reality check about the limits of American power – led indirectly to peace in the Gulf, an end to the Iran-Saudi proxy war in Yemen, and spiked the guns of US and Israeli hawks who have pushed so hard for war with Tehran.