In his recent commentary, David Trachtenberg called for more diversity in America’s missile defense systems and claimed that the current U.S. missile defense program “is but a shadow of the robust program needed to protect the nation.” (“U.S. Benefits From Diversity in Missile Defense,” Roll Call)

In fact, under President Barack Obama, missile defense is much more diverse and extensive than it was under President George W. Bush. The Obama administration has sustained the Ground-based Midcourse Defense System in Alaska, and it’s working to add 14 more interceptors there, even though the performance of those interceptors gets worse and worse each time they are tested, when it ought to be getting better.

The administration ought to replace those interceptors instead of building more of the bad ones. Moreover, it makes little sense, especially at a time of constrained defense budgets, to continue to invest in a failed system that doesn’t work and ought to be scrapped, as recommended last year by the National Academy of Sciences.

In 2009, the Obama administration also established the Phased Adaptive Approach in Europe, a much more diverse and extensive missile defense program than the Bush administration’s proposal for Europe. Where the Bush proposal included just one radar and one interceptor site in Europe, the Obama Phased Adaptive Approach includes radars in several locations and interceptors based on land as well as at sea.

In addition, the Obama administration is developing two regional missile defense systems, one in the Middle East to defend U.S. allies from Iran and another in Asia to defend U.S. allies against North Korea. If diversity is what Trachtenberg wants, he should vastly prefer the Obama approach.

As for the systems that have been canceled that Trachtenberg laments, such as the Airborne Laser, the Kinetic Energy Interceptor and the Multiple Kill Vehicle, they were canceled by Defense Secretary Robert Gates for good reasons under Bush, not by Obama. They were terminated because they did not and would not work.

Trachtenberg touts the need for a new sea-based platform to better defend against offshore threats and seems not to know that under Obama, the U.S. Navy has expanded its fleet of AEGIS destroyers and cruisers for missile defense and has deployed them worldwide from the Sea of Japan to the Mediterranean.

The problem with U.S. missile defenses is not that we need more platforms or more money, although building missile defenses in space, as Trachtenberg recommends, would entail hundreds of billions of dollars in costs that the tea party might question.

The problem with U.S. missile defenses is that they lack a workable architecture and many of the essential elements either don’t work or are missing, as reported by both the Defense Science Board and last year’s study by the National Academy of Sciences.

And the to-this-point-unsolvable challenge to U.S. missile defenses is their vulnerability to decoys, countermeasures, stealth and confusion from space debris from rocket stage separations; the slow pace of testing; and excessively scripted tests that avoid the realities of battle and impede effective operational capability.

A truly effective missile defense would deal with all these challenges rather than building systems that won’t protect American security.

Lt. Gen. Robert Gard (retired U.S. Army) is chairman of the Center for Arms Control and Non-Proliferation and former president of National Defense University. Philip Coyle is the former associate director of the Obama White House Office of Science and Technology and the Pentagon’s chief weapons tester under President Bill Clinton.