Last week the White House released its FY2015 defense budget. The good news: it addresses improving America’s homeland missile defenses. The bad news: The Missile Defense Agency is not quite certain about how to go about it.  That is dangerous.

To be sure, Secretary Hagel’s defense strategy, based on the Quadrennial Defense Review, leads off with: “Defending the homeland against all strategic threats.” Few disagree with such mom-and-apple-pie commitments. Fewer have time to actually assess strategic threats to the homeland, or the technology defending us from intercontinental ballistic missile (ICBM) attack.

Johns Hopkins School of Advanced International Studies says North Korea is building a new rocket able to strike deep into the continental United States. With help from North Korea, China, and Russia, Iran is also developing long-range rockets. The National Intelligence Council affirms that, “Most intelligence community agencies project that before 2015 the United States most likely will face ICBM threats from North Korea and Iran, and possibly from Iraq...”

Concerned about such threats in 2002, President George W. Bush ordered rapid construction of a ballistic missile defense system. By 2004, the Ground-based Midcourse Defense system (GMD) was in place with the first 8 interceptor missiles. The Government Accounting Office reports the investment in GMD reached $36 billion by 2012, with another $4 billion programmed for 2013-2017. The system created by those funds is a technological marvel.

In simple terms, the GMD system -- like the Standard Missile-3 on Aegis ships -- destroys attacking missiles by hitting them with a “kill vehicle.” To accomplish that feat, GMD’s sensors first detect the launch of an ICBM threat. When the incoming warhead approaches its midcourse, a Ground Based Interceptor rocket is launched towards it and, as its booster falls away, a small Exoatmospheric Kill Vehicle (EKV) remains hurtling through space, onboard sensors and thrusters guiding it to the ICBM warhead. The two objects collide at 15,000 mph, and the warhead is destroyed. It is like hitting a bullet with a bullet.

The U.S. has demonstrated that kill vehicle technology can and does work, with 34 successful GMD and SM-3 kill vehicle test intercepts. However, the haste with which the GMD system was built has caused problems. Drastic cuts by the Obama administration of maintenance, test, and development funding has also contributed to the failures. Senator Kelly AyotteKelly Ann AyotteAudit finds US Defense Department wasted hundreds of millions of taxpayer dollars US sends A-10 squadron to Afghanistan for first time in three years No, the US did not spend million on a gas station in Afghanistan MORE (R-N.H.) has noted that, “The Administration and Congress have failed to prioritize missile defense programs... from 2008 to 2012, funding for the GMD has been cut in half.” Such budget cuts make it impossible for contractors to make significant upgrades to their systems.

In the most recent test, July 5th 2013, the kill vehicle failed to intercept a target missile. The outcome of the ensuing debate over the future of the GMD system is crucial to the safety of the American homeland from long-range missile attacks.

On one side of the argument are those like Under Secretary of Defense Frank Kendall. He recognizes the cause of failed intercepts largely rests with rushed test and development. But he also thinks the solution is not to improve the current design, but to waste the billions already invested and to develop a completely new “Common Kill Vehicle.”

On the other side are quietly anonymous Capitol Hill staffers and other experts who agree a new kill vehicle should be built. But they also believe existing vehicles should be tested and upgraded first, because developing a totally new Common Kill Vehicle from scratch will cost billions, take ten years to deploy, and leave the homeland vulnerable to ever-increasing ballistic missile threats.

Director of the Missile Defense Agency, Vice Admiral James Syring, is well aware of that vital debate, and was questioned about it when his $37 billion budget was released. He affirmed that the GMD system will be tested again in the summer, that existing kill vehicles will be improved, and that research on a common kill vehicle will begin, but evaded describing the path forward. Kicking the can down the road, Admiral Syring has insured that lobbyists and Powerpoint slides will confuse Congress for months, if not for years.

It is very unlikely Congress will approve the budget as submitted, but the question remains: Do we keep our flawed missile defense for ten years while Iran and North Korea finish their ICBMs in two years, or do we improve our defenses first, and then decide whether or not entirely new kill vehicles are needed? If “defending the homeland against all strategic threats” is in fact Secretary Hagel’s top priority, then the answer is clear.

Nagle is a former Pentagon official, a director of The Committee on the Present Danger, and author of “Iran Covenant.”