Having spent much of my government career in the nuclear weapons community, I’ve watched with fascination as Donald Trump has called for the development and deployment of what he refers to as an “Iron Dome” missile defense shield to protect the whole of the United States. This is not some passing fancy, but something he brings up repeatedly, something that mattered enough for him to insist on its inclusion in this year’s Republican platform.

The incoming president’s reasoning, simply enough, is that if other countries can have such protection, then why can’t we? We are, after all, still the most scientifically capable nation on earth, at least when we set our minds to it. For what it’s worth, I think he’s absolutely right, and I think that this should be a major national security priority for the Trump presidency.
Is it feasible?
There have been, of course, many commentators who’ve observed, sometimes pungently, that it can’t work for us, that its radar coverage and missile response times are optimized for tiny Israel and cannot be scaled up to cover a continent-spanning nation. This seems to me a “strawman” argument. Trump clearly has something more in mind, a broadly-based research and development program for a system — or, more likely, a system of systems — capable of working on a much grander scale.
It’s reminiscent of Ronald Reagan’s Strategic Defense Initiative (SDI), ridiculed in its time by pundits with the “Star Wars” tag, but in retrospect viewed more positively. However limited in number, we do have anti-missile defense systems in place that would never have existed if these pundits had won the day. We may not be able to stop an all-out missile attack from Russia or China, but the systems in place might well suffice against the lesser capabilities of Kim Jong Un’s North Korean regime — and that’s nothing trivial. Nor, at a tactical level, would we have the capability demonstrated by U.S. warships in the Red Sea to swat down repeated Houthi missile attacks...