Imagine being stuck in a grocery checkout line for 33 minutes. Or in a traffic jam. Time would slow to a crawl, each minute feeling longer than the one before it.

But consider the fact that 33 minutes is also how long it would take for a long-range missile fired from North Korea or Iran to reach the United States. Then you realize how short that span of time actually is.

“We need to take action to respond to threats, and the ballistic missile threat is clear, and present, and growing,” says Robert Joseph, who served as Undersecretary of State from 2005 to 2007.

We’re very good at responding when we’re attacked. Look at how America rallied when Japan bombed Pearl Harbor, or when al Qaeda destroyed the World Trade Center and crippled the Pentagon. No one can doubt our resolve when provoked. With good reason did Adm. Isoroku Yamamoto warn that Japan’s actions at Pearl Harbor had awakened “a sleeping giant.”

But part of the job of providing for the common defense is anticipating threats, not merely reacting to attacks. And the fact is, rogue regimes such as North Korea and Iran are trying to get their hands on nuclear weapons.

Yet it’s easy to shrug off such warnings. Americans were more concerned years ago, when the prospect of a nuclear holocaust was new. The Cuban Missile Crisis in 1962 was a time of extraordinary fear. The 1980s saw popular culture saturated with warnings about the dangers of a nuclear arms race.

Fast forward to 2016, and people will admit to a bit of concern — if that. Have we become inured to the warnings just as technology has made the threat more real than ever before?

We ended the Cold War virtually without a shot. That’s a good thing, obviously, but wouldn’t it be ironic if we became victims of our own success? If that feeling of victory led us to become complacent?

In a way, we need missile defense more than ever. President Reagan knew that the ability to wipe out entire cities was the greatest danger we faced. So he wanted to make nuclear weapons obsolete. Hence the Strategic Defense Initiative, or SDI — a shield that would protect us.

As Mr. Reagan put it, “What if free people could live secure in the knowledge that we could intercept and destroy strategic ballistic missiles before they reached our own soil or that of our allies?”

Thirty years later, we have missile defense, but it’s not nearly as robust as it should be. We need components not only on the ground, but at sea and in space. A comprehensive system offers us the best chance of intercepting and downing a missile before it can launch its deadly payload.

“If an enemy of America had a ballistic missile, they could basically just hold America hostage,” says James Carafano, a defense expert who has taught at West Point. “If America wanted to go out and do something in the world, they could say ‘If you do that, we’ll shoot this missile at New York, or Los Angeles, or San Francisco’.”

We’ve seen the destruction caused by two planes in New York City on 9/11. Imagine a nuclear missile. And not just one hitting a city, as devastatingly effective as that would be, but one exploded at a higher altitude, which would create an electromagnetic pulse, or EMP.

An EMP is the giant flush of electrons and ionized particles that’s pushed out by a nuclear explosion. If exploded high over the center of the U.S., a missile could create an EMP that would incapacitate every electrical system in the United States.

Goodbye, cell phones, emergency medical assistance, and banking services. Just about everything that makes modern life possible would be gone in a flash. That’s what’s at stake, and why we need to step up our missile defenses sooner rather than later.

“The first duty of any national government is to defend the country and its people,” as former Attorney General Edwin Meese III puts it. If we don’t get that right, nothing else will matter.