Elder makes the case more eloquently than I can of what Trump's announced betrayal of the Kurds portends for us. However, I would like to call attention to another angle of the situation. In covering Turkey's plans to exploit the pending vacuum that Trump's withdrawal would create, the media describes Turkey as "deeming" the Kurdish forces to be terrorists. That terminology is wrong. Turkey certainly calls the Kurdish forces terrorists. However, that does not mean that Turkey actually considers them to be terrorists as opposed to believing that the Kurds' proper place is under the boot of Turkish and Arab oppression. What it means is that Turkey considers that the possibility that the Kurdish forces are terrorists is the most plausible explanation that could gain sympathy for its planned action. (Sort of like the Waqf describing Al Aqsa as "under threat" because it is more sympathetic than saying that it is Islam's right to deny Jews their holy sites.) Accordingly, the language that should be used to describe Turkey's motives is the Turkey "calls" the Kurdish forces terrorists.
Addendum: Trump apparently trusts Erdogan's word that he will not liquidate the Kurds wholesale in Syria. Needless to say, the Kurds in Syria do not concur in this trust, but Trump let his actions show whose views would carry the day.
Similarly, Obama trusts Abbas' that word that if he got all the land that is "rightfully Palestinian," that he would end his claims against Israel and end all attempts to pursue more. Netanyahu is cynical about such trust and acted accordingly. Obama, while he had the power to do so, let his actions show whose views would carry the day.