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There are essentially two sets of premises under which you could answer this question. The first is the real world, which contains likely threats to the American economy. Things like a deep recession that’s worsened by a credit contraction. Or oil prices that turn out to be skyrocketing not because of transient speculation, but enduring global instability and a dawning recognition of peak oil. Or a health system that isn’t fixed, and is chewing up 30 percent of our GDP in two decades.

The other set of premises is the fantasy world. This is more like Marvel’s “What If?” series. What is the Supervolcano explodes? What if we have an “I Am Legend” style pandemic? Or a “28 Days Later” zombie virus? What if “radical Islamic extremism” prevails and terrorists establish a global caliphate?

McCain chose…neither.

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Ezra Klein