The utility and value of missile defence systems remain unproven, but the United States plans to go ahead and deploy one in Eastern Europe regardless. The plan has delighted some former satellites of the Soviet Union, such as Poland, but irked other European nations, and remains of questionable relevance to US defence needs. Unfortunately, no one in Congress is saying so.

Defence officials say that ten interceptors in Poland and a radar in the Czech Republic are needed to protect the United States and its allies from yet-to-be developed Iranian ballistic missiles. But Russia's President Vladimir Putin believes that the shield has other purposes. On 27 April, shortly after a visit from US defence secretary Robert Gates, Putin announced that he would retaliate against the missile defence plan by pulling out of the 1990 Treaty on Conventional Armed Forces in Europe. US allies in Western Europe are irritated, meanwhile, that negotiations over the expansion will take place through bilateral channels, circumventing NATO.

But Democrats in Congress, who have long been suspicious of the missile defence system, are reluctant to oppose it. At Senate hearings last week, the Missile Defense Agency asked for nearly $9 billion in the next financial year, most of it to purchase early-warning radars and long-range interceptors, including some of the equipment for the European sites.

The panel's chairman, Daniel Inouye (Democrat, Hawaii), told the agency's leaders that they should be “proud” of their achievements and called for a beefing up of the system's capability. Two of the system's opponents, Dianne Feinstein (Democrat, California) and Byron Dorgan (Democrat, North Dakota), did raise specific concerns about its ability to detect decoys. But nobody was ready to side with Putin and publicly question the agency's plans to field the new interceptors.

That's unfortunate, because the missile defence project remains as technically questionable and strategically undesirable as ever. In tests, the interceptors have had mixed success at striking incoming warheads. Physicists have long been cautious about their effectiveness, and advocacy groups such as the Union of Concerned Scientists and the Federation of American Scientists continue to express deep scepticism over whether such a system can ever stop an incoming ballistic-missile attack. They think the system remains vulnerable to decoys and other relatively simple countermeasures.

Furthermore, this brittle defence can do nothing to stop cruise missiles of the sort already developed by Iran, nor can it intercept a warhead smuggled into the country on a truck or boat. In today's security environment, these threats are more direct than the long-range missile capability that Iran and North Korea do not yet have.

But last week's hearing suggests that missile defence may have become a pariah issue for the Democrats. Like gun control — an idea that cannot speak its name, even in the wake of last month's horrific shooting at Virginia Tech — the abandonment of missile defence seems to be politically out-of-bounds. Most leading Democrats are reluctant to oppose the programme — a form of defence that some polls suggest Americans mistakenly think they already have — in case it makes them look soft on national security. Nobody wins elections by dispelling illusions of security, and a few billion dollars is a small price to pay for political expediency, at least where Pentagon budgets are concerned.

But if the system is sham, as well as a menace to foreign relations, no more money should be wasted on it. Instead of humbly waving the programme's massive budget through, Congress should be asking the Government Accountability Office to establish exactly what US taxpayers have got for the tens of billions of dollars that the Bush administration has expended in pursuit of this myopic vision.