Congressional deliberations regarding missile defense sometimes appear driven more by theology than common sense. Some recent evidence: on July 23, the House of Representatives voted to preserve funding for an East Coast missile interceptor site—even though the military says it does not need or want that site now, and the interceptors that would be deployed there have not had a successful flight-test in five years.

U.S. policy since the early 1990s has sought to defend the United States against a limited ballistic missile attack that might be mounted by a rogue state such as North Korea or Iran. That lowered the bar from Ronald Reagan’s goal of an impenetrable shield to protect America against any ballistic missile attack, but it reflected the reality that the United States had neither the technology nor the resources to realize Reagan’s vision. Notwithstanding the fact that the technology remains elusive, the missile defense idea exerts a powerful attraction on many.

The George W. Bush administration came to office in 2001 eager to do something dramatic on missile defense. It rushed to deploy ground-based interceptors (GBIs) even before their test and development program had been completed.

Today, 30 GBIs are based in Alaska and California. When tests of GBIs equipped with a more modern Exo-Atmospheric Kill Vehicle (EKV) failed in 2010, Defense Department officials suggested there was no need for concern, as most deployed GBIs were equipped with an older EKV. Unfortunately, on July 5, a GBI test with the older EKV also failed. Since December 2002, the GBI has had only three successful intercepts in nine tries, not counting one failed test when the target did not reach the designated area. The GBI has had no successful flight-tests since 2008.

Intercepting a long-range ballistic missile warhead with a kinetic energy kill vehicle, which literally flies into the warhead, amounts to trying to hit a bullet with a bullet. This is rocket science, and it is exceedingly hard. The United States has poured tens of billions of dollars into the task over the decades. While the U.S. military has had some success at intercepting shorter range missiles, which travel at slower speeds, offense still holds the upper hand over defense when it comes to long-range missiles. That may frustrate missile defense advocates, but it is what it is.

The focus now should be on getting an interceptor that can work reliably. That means fixing problems with the GBI, though some have suggested instead replacing the GBI with a faster interceptor carrying a more advanced kinetic kill vehicle. The Missile Defense Agency needs to figure this out in a deliberate way. Haste makes waste, and the haste with which the Bush administration deployed GBIs is a big reason why the United States currently is stuck with interceptors that apparently don’t work very well.

It is thus odd that Congressional supporters of missile defense now want to devote funds to a new site to house these same interceptors on the East Coast. They assert that such a site is needed to protect the eastern United States from an Iranian attack, ignoring the head of the Missile Defense Agency, who wrote in June that “there is no validated military requirement to deploy an East Coast missile-defense site.” Rather than pushing for a new deployment site, wouldn’t it make sense first to get the interceptors to work?

We have some time to get things right. First, if necessary, the GBIs in Alaska are capable of engaging an Iranian ICBM warhead. That can be difficult to grasp unless you get a globe and take a polar view: Alaska is closer to the track of an ICBM warhead traveling from Iran to New York than one would think. (The big question, of course, is whether the GBI could hit the warhead.)

Second, today neither Iran nor North Korea has an ICBM that could reach the United States. The longest range missile in Iran’s inventory has a range of about 2000 kilometers, which would leave it well short of U.S. territory. The longest range missile that North Korea has successfully tested has a range of only 1300 kilometers. That could reach South Korea or Japan, but it would fall well short of even the Aleutian Islands.

A country does not get an ICBM overnight, unless it chooses to deploy an untested missile. A serious military first pursues a serious testing program, which would take time and require multiple flight-tests. Were Iran or North Korea to conduct ICBM flight-tests, they would be very visible.

Moreover, one should think of a missile defense system as an insurance plan. It gives the United States some capability—how much we do not know and can debate—for the future case in which Iran or North Korea might have an ICBM and decide to launch it at the United States. That is not a high probability event. U.S. missile launch detection capabilities would quickly pinpoint where the missile came from, and U.S. retaliation would be assured. For all their belligerence, does Iran or North Korea really want war with the United States, one in which they would invariably be crushed? The insurance plan would apply in that most unlikely case.

Building a workable missile defense system to protect the United States against limited ballistic missile attacks is a sensible objective. But given the evident technical challenges and the competing demands for U.S. defense dollars, it would be wise to pursue missile defense in a prudent way.