As always in the realm of national security, we do not know what we do not know. But one thing we do know–perhaps not to a certainty, but to a high degree of probability–is that next year, or in the next few years at most, unless it is stopped by diplomacy or force, Iran will develop a nuclear weapon. We also know, or should know, that if we permit this catastrophe to happen, we will urgently need defensive weapons to protect ourselves and our allies.

But are programs to develop such weapons on track, or are they being held back by those who would prefer to keep us defenseless?

Much in the news recently, on account of Vladimir Putin’s harsh reaction to it, has been one European component of such a defense, involving a radar station in the Czech republic and interceptor missiles based in Poland.

But the Pentagon has also been developing an Airborne Laser. Carried aboard a Boeing 747, it would be primarily aimed at stopping shorter-range ballistic missiles that could strike allies in Europe or the Middle East, including Israel.

The actual development and testing of an Airborne Laser was first funded in 1996, and the system has made considerable progress in the decade since. Earlier this month, an aircraft equipped with a low-powered laser was able to simulate the operation of a chemical high-powered laser of the kind that is already quite workable on the ground. Here, according to airforce-technology.com, is how that high-power system would work:

The primary laser beam is generated by a megawatt Chemical Oxygen Iodine Laser (COIL) located at the rear of the fuselage, which lases at 1.315 micron wavelength. The high-power laser beam travels toward the front of the aircraft through a pipe. The pipe passes through a Station 1000 bulkhead / airlock, which separates the rear fuselage from the forward cabins. The high-power beam passes through the fine-beam control system mounted on a vibration isolated optical bench. Beam pointing is achieved with very fast, lightweight steering mirrors, which are tilted to follow the target missile.

When the laser beam hits the target missile, it will heat a spot on its fuel tank, causing catastrophic failure in the missile during its boost phase, leading it to fall back with a bang onto the country that launched it.

Of course, as with any major new weapons system, there are technical problems, uncertainties, and issues involving trade-offs and costs. But the fact remains that more than thirty countries have some 10,000 or more ballistic missiles in their arsenals. Some of them are hostile. Some of them are very hostile. Though Iran is the most significant menace, it is not the entire problem.

Existing plans call for a “lethality test” of the Airborne Laser in 2009–right around the corner–entailing the actual shoot-down of a live missile. This if successful, would then allow us to use the system almost immediately in a national emergency.

Which makes one wonder all the more why the now-Democratic-controlled Congress, according to the indispensable Aviation Week & Space Technology, wants to cut funding and delay this lethality test by two years. This delay, unsurprisingly, has not been discussed in the mainstream media at all. What is it all about?

Ever since Ronald Reagan launched the Strategic Defense Initiative, widely mocked at the time by leading Democrats as a “Star Wars” fantasy, liberals have been reflexively opposed to missile defense. As the dangers have grown, many have moderated their rhetorical stance, and some have voted for experimental forays in this area. But a distinct lack of enthusiasm remains.

If the U.S. or one of its allies falls victim to a nuclear-missile attack that we are unable to avert, it will be much too late for finger-pointing at the people responsible for delaying–or killing–our defensive capabilities. It is better to do the finger-pointing now.