The fancy machine tools, materials, and components that were good enough to build the nuclear weapons of the 1970s are widely available now. My favorite example is that one of the machine tools linked to the A.Q. Khan network was a used Denn machine tool. If you go to the Denn website, they tell you what their machine tools can be used for: everything from armaments to kitchenware. And, be still Fareed Zakaria’s fluttering heart, auto parts. (Flow forming machines make sweet rims.) Talk about dual use!

The United States was deeply skeptical that Pakistan could build centrifuges in the 1970s because of the country’s limited industrial base. What U.S. analysts didn’t grasp was that Pakistan’s industrial base — and that of every other proliferator — was the entire world. There is no reason to think this problem went away with A.Q. Khan. Take a spin around Alibaba, the big Chinese online B2B procurement site sometime.

Moreover, a proliferator doesn’t have to try to acquire the most modern centrifuges. When U.N. inspectors were stumbling across the remnants of the Iraqi nuclear program in the early 1990s, they made a surprising discovery: Calutrons. These were an obsolete uranium enrichment technology (electromagnetic isotope separation) from the 1940s that fell out of favor after World War II. Inefficient, sure, but good enough to make the highly enriched uranium for the Little Boy bomb that destroyed Hiroshima.