Turkey is the biggest military ally USA have. Loosing it will be a "before, and after" moment for NATO.
Truly, USA's biggest problem with Turkey is exactly them being such a strong, and prominent military ally, throwing discord in US dominated bloc solely by the fact of its existence.
Points:
1. Turkey's ultimate political alignment is NATO
2. Turkey's current political position can be rationally understood, in comparison to more irate allies, playing their double, triple, quadruple games. It has tensions with NATO, and US, but not because its ultimate alignment, and commitment to Atlantic Bloc changed.
3. Turkey is a way more useful military ally US have than any EU NATO member. Both in military strength, and level of commitment.
4. Turkey is the sole country US can consider a real military ally among dozens of "ally" countries which USA buys with billions of dollars per year in defence aid: Saudis, Egyptians, Emiratis, Pakistanis, Jordanians, Israelis... they are all basically a $100B a year black hole for defence aid.
5. Turkey is the only non-white country with commitment to hosting American nuclear weapons, and other serious defence assets after South Korea, and Japan quit. This is currently American's sole proof of not seeking a "rich white world alliance" as its foreign policy vision — hugely symbolic.