It has taken eight months but United States President Barack Obama has now made a strategic foreign policy step that has put a few drops of clear blue water between his Administration and that of his predecessor.

The move last week to slash George W. Bush's Star Wars sequel is less an ideological feint leftwards than an exercise in pragmatic cost-cutting. Yet it is still a bold change.

Bush's defence system had a future price tag of US$5 billion ($7 billion), although Newsweek estimates the US has spent more than US$150 billion developing such systems since the 1980s. It was prepared for a long-range missile threat that is yet to materialise and was a cold stone weighing down Washington's relationship with Moscow. It will be replaced with a cheaper, more realistic programme that takes advantage of mobile military capability.

Critics of the change have focused on the risky appearance of concession to the Russian Bear after Moscow's long opposition to the stationing of missiles in areas it regards as its sphere of influence. The Telegraph quoted Dan Goure, a Pentagon consultant, as saying: "The Administration's policy seems to be to give away first and negotiate second. That's not how it works with the Russians."

But as Fareed Zakaria points out in Newsweek, "to continue with a bad policy simply because the Russians don't like it is not a sensible basis for US strategy".

Still, it's a seismic shift away from the no-compromise, granite, immobile security certainties of the early Bush era - the Axis of Evil, the US does not (officially, bilaterally) talk to rogue states, you're with us or against us ...

Missile defence, whatever its impracticalities, carried symbolic power. In Defence Secretary Robert Gates' words: "When it comes to missile defence, some hold a view bordering on theology that regards any change of plans or any cancellation of a programme as abandonment or even breaking faith."

But part of the reason why the decision has a special impact is that up until now the Obama Administration has largely resembled the less-ideological fag end of Bush's rule - the regime that was involved in multilateral Iran talks, that prodded North Korea through the six-power framework, that trod the Middle East in search of a two-state solution.

Differences between the administrations on foreign policy have been more a matter of nuance and aspiration than anything definitive.

* Obama has deepened America's involvement in Afghanistan without revealing any strategic cards to deal an exit.

* The withdrawal from Iraq is proceeding along the lines of candidate Obama's get-out clause - that he would take military advice on its pace - and is essentially keeping to Bush's timetable.

* The "war on terror" is being prosecuted just as fiercely as before on Pakistan's border (and Somalia) even if it's no longer called the "war on terror". The Guantanamo detention centre is to be closed but detainees' fates are still being decided. Other lockups remain. Detainees at Bagram will now get Bush-style military lawyers. Renditions continue, just with greater oversight from the State Department.