Ballistic missiles pose an increasing risk to the United States and its allies, particularly as more nations strive to acquire nuclear weapons. The once exclusive nuclear weapons club now has nine members, and Iran is knocking on the clubhouse door. Altogether, at least 32 countries have ballistic missile capabilities.

Defending the United States, its forward-deployed troops, and its friends and allies against such threats should be a national security priority for the U.S. president. We have a fledgling missile defense capability. But further investment, research and procurement are needed to truly realize a fully effective ballistic missile defense (BMD) system.

The growing threat of missile and nuclear attack is particularly acute in East Asia. Diplomacy has failed to stop North Korea from developing nuclear weapons and the missiles to deliver them. North Korea’s extensive ballistic missile force can now strike South Korea, Japan, and U.S. military bases in Asia. Its ongoing long-range missile program could threaten the continental United States by 2015.

China has expended enormous effort in developing long-range missile forces with a precision strike capability that places a large variety of targets at risk through-out the Asia-Pacific region.

Washington has sought to develop common missile defense policies to defend Asian allies against missile attacks from North Korean and Chinese launch sites – but with mixed results.

America and Japan have made considerable strides in BMD cooperation and interoperability. Tokyo has developed and deployed a layered, integrated missile defense system consisting of sea-based SM-3 interceptors for high-altitude missile defense and land-based PAC-3 units for terminal phase interceptions.

On the other hand, liberal South Korean presidents from 1998-2007 downplayed the North Korean danger, and Seoul resisted joining an integrated missile defense system with the U.S.. Instead, it has built only a low-tier missile shield of older German Patriot-2 missiles and Aegis destroyers without theater ballistic missile capability.

Seoul’s reticence about defending itself against the North Korean threat changed dramatically with the election of conservative President Lee Myung-bak in 2007. However, President Lee must follow through with requisite actions, including contemplation of a comprehensive regional network with the United States and Japan.

America’s European allies are also vulnerable to ballistic missile attack. The United States has a mutual defense clause with its 27 fellow NATO members. A ballistic missile attack on any one member could therefore, potentially involve the U.S. in military action. It surely makes greater sense to deny a potential aggressor the means of attack in the first place.

Many NATO members have taken tentative steps to build components of what could eventually become a comprehensive missile defense architecture, such as the Patriot air defense system. However, European nations must do more to adequately protect their populations and territory from the risk of missile attack.

Turkey, Poland and Romania have all recently agreed to host elements of the U.S.’s missile defense architecture. As important as these bases will be, Europe’s contribution to transatlantic-wide missile defense must be about more than hosting U.S. sensors and interceptors. Truly effective BMD requires a layered approach capable of intercepting missiles in all phases of flight – boost, midcourse and terminal. Linking together members’ capabilities into a coordinated, layered defense is estimated to be just €200 million ($279 million) over 10 years.

Given the increasing global missile threat, the U.S. must reverse the budget cuts proposed for missile defense programs. Instead, we must significantly strengthen the land, sea and air components of U.S. missile defense.

A comprehensive missile defense would not only protect the American homeland, but also reassure our friends and allies. Missile defense contributes to regional peace and stability and supports international nonproliferation efforts by reducing other nations’ perceived need to acquire nuclear weapons. It is a win-win solution to one of today’s greatest security threats.

Bruce Klingner is senior research fellow in the Asian Studies Center at The Heritage Foundation. Sally McNamara is senior policy analyst in Heritage’s Thatcher Center for Freedom.

Cross-posted from as part of its series in run-up to the November 22 GOP debate hosted by The Heritage Foundation and the American Enterprise Institute on CNN.