Rupert Cornwell: A political manoeuvre that allows President to take moral high ground

President Obama's new Nuclear Posture Review is above all a political statement, not a military one. For all the administration's trumpeting of it as a "milestone" in US nuclear doctrine, and the limitations the review imposes on the circumstances in which the US might use actually nuclear weapons, it hardly changes the likelihood of that happening.

But the document – the third of its kind since the end of the Cold War – makes three key political and diplomatic points. First, it recognises that the biggest nuclear threat to America comes from rogue states and terrorist groups, not from established nuclear powers like Russia or China. From this flows the second objective of the review: to reduce the risk of nuclear proliferation, the subject of a United Nations conference in New York next month.

Third, and most ambitious, it is another step towards the nuclear free world that Mr Obama set out in April 2009 during his speech in Prague. And as with any political document, context is everything.

The review was released 48 hours before Mr Obama was due to sign the new Strategic Arms Reduction Treaty (Start) with Russia, reducing their arsenals of deployed warheads by 30 per cent. It also coincides with new efforts by Washington to secure tougher sanctions against Iran, public enemy No 1 in terms of rogue states with nuclear weapons ambitions.

Not by accident, US officials yesterday singled out Iran and North Korea as exceptions to its commitment that Washington will not use nuclear weapons against a non-nuclear state, even in retaliation for a chemical or biological attack. Finally, the review is a sign of US intent ahead of next week's 40-nation nuclear security summit here.

In military terms, the promises make little difference. Even assuming the replacement Start treaty is ratified, which is no sure thing, the US will still have more than enough nuclear weapons to deal with any conceivable threat.

In political terms, however, the pledges are highly important. Along with the Start cuts, they enable Mr Obama to claim that, as his country lectures the rest of the world about non-proliferation, it is reducing its own stockpiles. George W Bush also sought to reduce America's nuclear arsenal, but he undercut his case by leaving the door open for the development of new generations of even more destructive weapons. Mr Obama has shut that door.

In an ideal world, the President could have gone further. But the real US political world, where important mid-term elections are just seven months off, is populated by conservatives waiting to pounce on anything allowing them to portray Democrats as soft on national security. As the President noted in Prague, he is "not naive" about the difficulties in the way of a world without nuclear arms, warning that it might well not occur in his lifetime. That remains no less true, even after yesterday's announcement. But the review is a small step in the right direction.