I'm not arguing you think that. I'm using the power of sarcasm to note that Trump is not the sort of person who would amass a load of good intel, analyse it thoroughly and come up with a great plan, and it doesn't seem like anyone in his administration did the hard work and told him either. Thus even the argument he carried out "good" policy would be that he lucked on to it.
What went on in the phone call between Trump and Erdogan (6th Oct?) is only known from sources such as "one senior administration official", but it seems Erdogan said he wanted to launch an offensive against the Kurds, and Trump promptly ordered US troops out of the affected zone. This was so sudden, unexpected and rapid that the US forces didn't have time to clear their camps properly and ended up bombing them to make sure there was nothing sensitive left. No-one in the US government seems to have known or were ready, never mind the Kurds, who were forced to flee in haste.
The letter was sent on 9th Oct, the same day Erdogan sent troops over the border. It is bizarre. My guess here is that between the 6th and 9th, Trump looked upon the massive Washington shitstorm as policy advisors, the Pentagon, both parties in Congress, the media and much of the population shouted "WHAT THE FUCK???" and he went into full on panic mode, dictating a rather emotional overreaction - but by then, it was all too late.
I think the idea that the USA might pull out its troops at some point reasonable and to be ultimately expected. What I don't think anyone could have accounted for is that it would be done in such incredible haste with no discussion or preparation - not with the Kurds, European allies, the Secretary of Defence, Pentagon, etc. And clearing the way explicitly for the purpose of an offensive launched against he Kurds, too, without even the grace of trying to mediate a better working relationship between them and the Kurds, as a middle option, either? Cold, callous, betrayal that cost plenty of lives and displaced hundreds of thousands from their homes.
From my perspective, it utterly beggars belief that the president of the USA can't even do something as basic as tell the president of Turkey he can wait another few weeks. Do we really think Turkey is going to take the risk of running an offensive past US bases and killing US personnel?
Of course it wouldn't. But I think Erdogan had Trump's number. Trump's a business dealmaker, a people-pleaser, admires and desires approval from strongmen like Erdogan. Trump likes his personal relationships, chummy man-to-man agreements, favours and back-scratching. I suspect Trump just doesn't get governance, that the state is not his personal fiefdom, that there are principles and national interest, other people's welfare to consider. In fact, that's probably what really hurt Trump, re. the anger in the letter. He realised he, "master of the deal", had been a dupe and Erdogan had played him.