Afghanistan is a small country but its position in US's hegemony is critical. A 20 year war that together with Iraq bankrupts US. The same kind of war killed USSR. If this war is a mere peripheral problem or inconsequential, then there is nothing existential.
If you define "existential" at the US territorial boundary, then China is just a peripheral problem. If you define "existential" as the US global hegemony, then Afghanistan is equally important as China, it is a milestone to contain China and Russia.
that is a stretch so epic songs will be written about it.