Leading article: A sensible retreat by Obama

All sorts of reasons will no doubt be posited for President Obama's decision to abandon his predecessor's plan to build a missile defence system in Poland and the Czech Republic. The Republicans in Washington have already castigated it as an act of cowardice, giving in to Russian pressure. The Czechs and the Poles (or at least the parties that approve it) have expressed concern that it represents a loss of interest by the new US President in European defence. The Russians have understandably welcomed it, albeit cautiously, as the removal of a major stumbling block in their relations with Washington.

The reason for the reversal of US policy, however, is likely to have been rather more straightforward. As a defence project the system, due to be installed by 2012, was expensive (it has already cost over $100bn) and unproven. Even the fear of a rocket attack from Iran, the ostensible purpose for putting in a new weapons system intended to bring down incoming rockets before they landed, was receding. Iran has proved slower than expected in developing long-range missiles (if, indeed, it regards them as a priority at all).

Meanwhile the political problem of proceeding with installations right on Russia's borders were growing more troublesome, not just in relations with Moscow but also within Europe itself where a number of countries, including Germany, were far from convinced that the military need outweighed the political cost.

That calculation in the end is probably what convinced the new President, who had been elected expressing his doubts on the plan, finally to pull the plug on it yesterday. It is a sensible decision, but one which still leaves an open-ended question so far as European defence is concerned. Relations with Russia will certainly improve. It could also help ease the atmosphere for the talks due to start with Iran next month. But the removal of what has been a distraction to Europe and NATO also poses the problem of where the EU should go next in building up its own defences. Washington has made clear its belief in regional investment in new anti-missile systems. Europe is still dithering. It shouldn't be. Obama's about-turn has put the ball firmly in our court.