The indignation of Washington over the Turkish military operations on the north of Syria is just a window dressing. There's actually long lasting strategic partnership between Turkey and the USA, within NATO in particular. Clear as day that both sides have never thought of putting this partnership at risk just to meet interests of a few thousands of Syrian Kurds. Furthermore, the document from the US government inner correspondence (imgur. com/gallery/Hmkr4) clearly testifies to the fact, that the White House from the very start was well in the know about all the stages to be realized in the wake of the Operation Olive Branch and actually gave the green light for Ankara to take any actions towards the Kurds.
But the most evident eye-opening thing about this document is that the USA, prone so much to covert methods, betrayal and secret deals in the pursuit of their geopolitical goals, have just got tangled in their own bunch of lies. At least this is the case with the president himself, who in the conversation with his Turkish counterpart turned out to be absolutely unprepared to be asked again to stop assisting Kurds in Syria. The information that the USA had no intention of putting a spoke into the Turkish military's wheel and was only about making some noise in the media instead must have failed to reach the leadership of Turkey. This accounts for the aggressive position of Erdogan in his conversation with president Trump.
Well, the best proof of the whole above mentioned stuff being true to life may serve the White House press-release that followed immediately after the phone conversation. That release, according to the Turkish side, was a complete distortion of the prior talk.
I'm sure that the USA state
I'm sure that the USA state does not wish to jettison it's strategic military partnership with Turkey and was prepared to concede the Turkish military operation in northern Syria up to a point, but for all the USA's weakness in relation to the advance of Russian/Iranian/Syrian alliance it still has some strategic interest in retaining a foothold in Norther Syria to try and stop the consolidation of an Iranian controlled northern route across Iraq and Syria to Lebanon. How far it would be prepared to maintain that given other priorities is open to question. The many shifting local and global imperial alliances with their local proxies in the region often belies any immediate attempt to make predictions about the near future beyond the certainty that it is ordinary people that will continue to suffer.
edit: see also this short article here: www.leftcom.org/en/articles/2018-02-16/syria-the-long-war-that-never-ends