In his efforts to Make America Great Again, Donald Trump has succeeded in reviving at least one aspect of America’s past: the fear of nuclear war. Since taking office, the president has boasted about the size of his “Nuclear Button,” jettisoned the nuclear deal with Iran, and threatened to unleash “fire and fury like the world has never seen” on North Korea. His national-security adviser, John Bolton, openly advocates a first-strike policy against nuclear-armed enemies, and the Pentagon, after decades of careful disarmament, wants to spend $1.2 trillion to upgrade its nuclear arsenal. If you’ve felt a new shiver of nuclear fear over the past year, you’re not alone: The Bulletin of the Atomic Scientists has moved its “Doomsday Clock” to within two minutes of midnight — closer than it has been since the height of the Cold War. In January, when a state employee in Hawaii mistakenly triggered an emergency alert, warning that a ballistic missile was inbound, many islanders raced to take shelter and unite with their loved ones, believing they were only minutes away from utter devastation.

What made the false alarm all the more frightening is just how plausible the prospect of a nuclear strike has become. The U.S. and Russia, both of which maintain massive nuclear arsenals, are increasingly at odds. Iran has announced plans to ramp up its production of enriched uranium. North Korea may already have nuclear missiles capable of striking anywhere in the U.S., and there is no way to know whether Trump’s negotiations with Kim Jong-un will wind up increasing or decreasing the prospect of nuclear war. But the current state of dread, while entirely understandable, has overshadowed two crucial realities about the threat of a nuclear calamity. First, a nuclear attack on the United States could well come not from the skies but from the streets. Experts warn that it would be relatively easy for terrorists to build an “improvised nuclear bomb” and smuggle it into America. Building a ten-kiloton bomb nearly as destructive as the one dropped on Hiroshima would require little more than some technical expertise and 46 kilograms of highly enriched uranium — a quantity about the size of a bowling ball.

The second reality we have failed to understand is what a nuclear detonation and its aftermath would actually look like. In our imaginations, fueled by apocalyptic fictions like The Road and The Day After, the scale and speed of nuclear annihilation seem too vast and horrific to contemplate. If nuclear war is considered “unthinkable,” that is in no small part because of our refusal to think about it with any clarity or specificity. In the long run, the best deterrent to nuclear war may be to understand what a single nuclear bomb is capable of doing to, say, a city like New York — and to accept that the reality would be even worse than our fears.

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