The unanswered question is what, if any part is the S400 Russian Anti-Aircraft system delivered to Turkey despite American protestations summer of 2019 playing in the pull back of the American soldiers from the forward Kurdish areas?
The S400, a terribly expensive system developed by the Russians specifically to defeat NATO air power, even the new F-35, was delivered to Turkey complete with Russian advisors sometime around July 2019 according to reports.
If the S400 is deployed defending the invasion of Kurdish held regions by the Turkish army, American air cover normally brought in to protect ground assets by establishing a no-fly zone is significantly degraded.
Air cover turned back Saddam Hussein during Gulf War 1. After the Iraqi army was run out of Kuwait, Saddam turned his wrath on the Kurds. Using air power, America completely subdued the air assault by creating a no-fly zone. 10’s of thousands of Kurds were saved from certain annihilation.
Whether Turkey holds that advantage now or not, the President is probably well aware.
Turkey no longer appears to be a committed member of NATO.