Dispatches from Afar

I want to focus on a side comment in this post from Gregory Djerejian:

Unlike Vietnam then, where the domino theory proved a chimerical fear, an American departure from an Iraq still unsettled and cascading into potentially greater chaos could serve to further radicalize the region...

[Emphasis mine.]

I'm not convinced this is the right lesson. Two of the three nonaligned adjacent nations (Cambodia and Laos) did indeed fall to Communist dictatorships, with terrible consequences. It would be more accurate to say that our defense against a domino scenario fell back to a prepared position, off the shores of Thailand, which had been strengthened by our long involvement in Vietnam. [Something like this.]

Where is our second line of defense in the current struggle?