nytimes ed. board:

...

The president just doesn’t seem to get that any American withdrawal requires careful thought to ensure we don’t surrender the gains we’ve made, endanger troops on the ground or alienate our allies. What will happen, for instance, to Syrian Kurds who have been crucial American partners in fighting ISIS and now are under attack by Turkey, which considers the Kurds to be terrorists? Or to Israel, which is increasingly concerned about the foothold that Iran, an Assad ally that Mr. Trump has decried as a major regional threat, has gained in Syria?

Besides Iran, another notable American adversary is likely to benefit from the president’s apparent desire to retreat from the Middle East: Russia. Already, Mr. Trump is letting Russia take the lead in Syria, ceding to Vladimir Putin the crucial diplomatic work of forging a political agreement between Mr. Assad and the Syrian rebels. Mr. Putin, an Assad ally, met Iranian and Turkish leaders in Istanbul on Wednesday to plan Syria’s future. How does that serve American interests?