But who in US, how, why? What they want to achieve in the end? We live in interesting times.
This all started after the election of Trump.
Trump has repeatedly said that he will end American engagement in Ukraine, europe and middle east. Instead, people behind Trump wants to rigthfully concentrate on China. They realize that Chinese industries are talking over a lot of their previous industries, markets and creation of an alternative payment system (which is also supported by Turkey) will be the end of american world currency status or hegemony.
If America lose the world currency status, Usa will see double digit inflation for long time, creating internal problems.
America have about 10 years until China reach economic and possibly military parity (in Asia) with USA. As a valid response to these concerns, USA is shifting her engagement towards China, leaving Middle East + Europe. This engagement have the very high probability to become a hot conflict so they need to ramp up all the propaganda machines in west. USA is openly pushing hard for an open conflict with China.
However, current American officials realize that they cant just leave Middle East without securing their gains, including for Israel. So they really have to limit Iranian (=future Chinese) influence as much as possible around Israel. the rest of Arab countries are easily controlled dictatorships.
Hence, the current Biden+pentagon officials allowed the current Turkish operation against Assad to limit iran/russia/Chinese in Middle East before trump takes office as he could abruptly order a complete evacuation without any planning for the future.
Keep in mind that USA+EU have always been against any Turkish operation in this region but they are very very quiet this time. Much of the problems in Syria and EU including Brexit would not have happened if Usa+Eu had they listened on Turkey 10 years about creating safe zones in syria. EU+Turkey would have 5 million less refugees and potentially would have had a significant effect on the Ukranian war. Life is a bitch sometimes with unintended consequences. this time, these consequences can cost America their world currency domination in the long term by being bogged down in middle east and ignoring China for the last 25 years.
In essence, this is a combined Turkish, American and Israeli operation to protect american influence in the region for a potential future hot war with China. For Usa, it is better that Turkey is taking over the the role as dominant power in Syria, Lebanon, Palistine than Iran (=future china). Israel can not be allowed to take over as that would just ensure a continued war and american engagement for another 50 years.
Concerning YPG/PKK/KCK, i don't know if trump/americans will keep protecting them against Turkey or throw them under the buss. We will see in the next few weeks but talks about Ocelan in the turkish parliament indicate that we will not be allowed to touch certain regions but take over some (like mumbic/tel refit). We will see in the next few weeks about these plans.
Ps. As a side note, allowing Turkey back into the F35 project is also part of the overall strategic changes in recent years by both Turkey and Usa.