The picture below accurately describes Trump's decision on Syria:
Here is a quick summary of the key ramifications of Trump's decision:
1) Pompeo and Pence are traveling to Turkey to negotiate a cease fire
2) Trump has threatened Turkey with sanctions
3) Foreign Minister Mevlut Cavusoglu says all threats and sanctions against Turkey over Syrian offensive are unacceptable.
4) our ex-allies, the Kurds, have now struck a deal with Syria's dictator, al-Assad. The pact, brokered by Russia, came hours after the United States announced it was pulling its troops from Syria to avoid getting caught in clashes between the Turkish military and the Kurdish-dominated Syrian Democratic Forces (SDF).
5) Trump is meeting with congressional leaders at 3:00 today, and opposition Democrats plan to vote on a resolution rebuking his decision to ditch our Kurdish allies.
6) Turkish president Erdogan has been trying to establish a "safe zone" in northern Syria since 2012. Operation "Peace Spring" is the third major Turkish military operation inside the country since 2016. Before 2016, Erdogan's plans to intervene militarily in Syria were opposed by both the Obama administration and the Turkish military, which the president did not yet have complete control over. Erdogan, as a result, declined to participate in the US-led war against the Islamic State of Iraq and the Levant (ISIL or ISIS), declared by Obama following the fall of Mosul, in the summer of 2014.
In January 2018, the State Department, under former Secretary of State Rex Tillerson, outlined a plan for a long-term US military presence in Syria. He defined four key objectives for the open-ended US military presence in northeast Syria. They included ensuring a lasting defeat of ISIL and al-Qaeda, creating the right conditions for the return of Syrian refugees, curbing Iranian influence in the region and holding UN-supervised elections aimed at securing a new leadership in Damascus. The latent motive behind this strategy, as Tillerson put it, was that the US "cannot repeat the mistake of 2011, where a premature departure from Iraq allowed al-Qaeda to survive and eventually become ISIS".
Trump was unconcerned. In March 2018, he fired Tillerson and the following month he took almost everyone off guard when he announced the full withdrawal of US troops from Syria.
Turkey took advantage of this schism within the US administration and opened a direct channel with Trump. Hence, by the end of the six month period, Erdogan had called Trump and received assurances that the US would soon be leaving. Trump was quoted as telling Erdogan during their December 2018 phone call on Syria: "It's all yours. We are done."
7) as a result of Turkey's invasion, over 700 ISIS prisoners have been released, in direct violation of the key objectives outlined by Tillerson.