Where Trump had done a deal with Erdogan while Ivanka was opening Trump Towers Istanbul and has disarmed the Kurd over the last few months for in return US 'protection' and this is their Trump thank you for helping to defeat ISIL by throwing the Kurds to the Turkish military in an invasion.
The reason that Trump has rowed back on his approval is that Turkey has previous on Kurd genocide in previous invasions which is a war crime that involves all culpable parties not only on direct action but also any third party 'approval' intent. When this was pointed out to Trump, he has sensibly reigned back his approval so he will not be liable for any war crimes committed by Turkey.
Where I'm certainly no fan of the Kurdish Marxist PKK terrorist group, I'm also no fan of Western countries using useful groups for their geopolitical dirty work and then selling them out to a bleak bloody fate as soon as the have served their purpose. This badly damages Western standing in the world and also gives the West's hard left like Corbyn ammunition on the 'wicked' right which makes the defence of centre-right conservative values much more difficult.
Once you understand that what drives Trump is his constant need for money where the cost of sustaining his lifestyle far exceeds what he has ever been capable of earning hence his numerous business failures and bankruptcies. Fortunately, his global money laundering operations are one of his rare successes and of great use to many of the world's corrupt leaders and dictators for parking 'clean' money in safe havens. Vlad, Semion et al are happy to keep paying the piper for his services as long as he keeps playing their tunes. This is big league stuff where $100m is small fry & $bns normal business.