President Bush is making clear that he intends to build America's first nationwide missile defense. Critics at home and abroad have moved swiftly to denounce it.
But what exactly is "it"? Mr. Bush's comments on missile defense during the campaign were long on rhetoric but short on substance. When pushed to specify what a Bush administration missile defense would look like, Mr. Bush's aides begged off.
President Bush no longer has the luxury of putting off the details. Filling in the specifics, however, will not be easy. As Mr. Bush's comments suggest, there are three competing visions of what any missile defense should attempt to accomplish.
One possibility is resurrecting Ronald Reagan's dream of a missile defense that renders nuclear weapons "impotent and obsolete." After meeting with the chief foreign policy adviser to Russian President Vladimir Putin last April, Mr. Bush said that America needed to protect itself and its allies "against any missile launch"— presumably even the remote possibility of an all-out Russian strike with thousands of warheads.
Another option is to try to build a system capable of defeating a deliberate Chinese missile attack. Such an attack might most credibly occur in the context of a war between the United States and China over Taiwan.
When asked during the campaign if he would build a missile defense to counter China's strategic missiles, Mr. Bush declined to rule out the possibility. In contrast to these two proposals to go "big and bold," Mr. Bush could push for a limited antimissile system designed to blunt the small and crude arsenals that countries like North Korea, Iran and Iraq might build.
On the eve of his inauguration, he told reporters that the technology and politics of missile defense "mean that initially we will be deploying systems that will prevent the accidental launch of ones and twos."
Which vision Mr. Bush embraces will be critical because it will determine what the United States needs to build, how much it will cost and how other countries will react. Mr. Bush faces pressure from Republicans to be ambitious. Most believe that the minimal goal for any missile defense should be to neutralize China's nuclear deterrent.
But going big and bold presents daunting obstacles. One is cost. Robust missile defense could easily cost more than $100 billion at a time when the Pentagon is unable to fully fund existing programs.
Another is technology. Scientists are trying to develop the ability to shoot down a single warhead equipped with one or two crude decoys. That is a far cry from the thousands of warheads armed with sophisticated countermeasures that Russia could rain down on the United States. China too could probably build good countermeasures.
A third obstacle is diplomatic. Neither Russia nor China is likely to sit still while the United States builds an antimissile system that could nullify their nuclear deterrents. The problem is not, as doves frequently claim, that they will launch an arms race. Neither could afford it.
Rather, the problem is they might retaliate with policies that discourage arms reductions, reduce safety and encourage proliferation. Moscow might suspend efforts to secure and downsize its frighteningly dilapidated nuclear arsenal, raising the risk that of terrorist threat or an accidental attack.
China and Russia might also refuse to help stem missile and nuclear proliferation. They may even sell countries like North Korea the advanced decoys need to penetrate any U.S. missile shield. In short, big missile defenses could actually aggravate the threat they are meant to counter.
The wiser course of action would be to build missile defenses that target rogue state missiles but present a minimal capability against Russian and Chinese missile forces. The key technology here is boost-phase defense. Unlike the Clinton administration's midcourse system, which attempts to strike down individual warheads in space, boost-phase interceptors would shoot down missiles shortly after launch, when they were slow and highly visible. This would also provide good protection for U.S. allies, whose security we have sworn to uphold.
To work, however, boost-phases defenses need to be located within several hundred miles of the launch point. That is not a problem with relatively small countries like North Korea and Iraq. Russia and China are another matter. Their great size means that a boost-phase antimissile system would not threaten their nuclear deterrents (unless it was a space-based system, but that technology is not presently within reach).
If Mr. Bush opts for a defense that is truly limited to blunting the potential threat that rogue states pose, he stands a good chance of carrying the day. But if he embraces visions of going big and bold, expect a debilitating political and diplomatic brawl, as well as a high price tag. On national missile defense, given current technological and strategic conditions, small is beautiful.