(edit: talking about whether Trump would defend Turkey if Russia invaded unprovoked): Trump said he would have to think about whether those countries “have fulfilled their obligations to us.” Trump clarified, “If they fulfill their obligations to us, the answer is yes.”
It seems pretty rational to me; he's saying that if a country like Turkey wants to acquire the benefits of a military alliance they need to pay their fair share. On the surface that seems reasonable to me and honestly, from reading here if Erdrogan got attacked by Russia I doubt most of Trump's enemies would shed any tears about his stance on NATO anyway.
[0] http://dailycaller.com/2016/07/21/trump-doesnt-care-about-er...