America has developed a new dependency on armed drones, pilotless aircraft guided from afar that can rain instant death from unseen heights. They've been used to kill more than 1500 people, including at least four US citizens, in a program of daily targeting and assassination.
It's a dependency driven by frustration. The US Congress expressed concerns last week at the fact the White House controls the system in great secrecy as the self-appointed judge, jury and executioner of people who have no right of appeal.
But consider the frustration of a president trying to crush al-Qaeda and subdue the Taliban. After seven years of war in Afghanistan, the US realised it needed to pursue the terrorists across the border to their hideouts in Pakistan, a country which is, notionally, a US ally.
George W. Bush ordered the firing of missiles from drones into al-Qaeda camps four times in the first half of 2008, respecting Pakistan's sovereignty by notifying the authorities in advance.
But the terrorists were scattering and the missiles were finding the camps empty: ''The US had uncovered evidence that the Pakistanis would delay planned strikes in order to warn al-Qaeda and the Afghan Taliban, whose fighters would then disperse,'' wrote Bob Woodward in his impeccably sourced 2010 book Obama's Wars: The Inside Story.
The US had intercepted calls from a colonel in Pakistan's intelligence agency, the ISI, tipping off a guerilla commander. ''Okay,'' Bush had said, ''we're going to stop playing the game. These sons of bitches are killing Americans. I've had enough.'' He stepped up the drone strikes, giving Pakistan notice only as they happened.
It worked. Drones, mainly Predators mounted with a pair of Hellfire missiles or the far bigger Reapers mounted with four missiles, have allowed the US to kill many of the key commanders of al-Qaeda and its affiliates in Pakistan, Yemen and Afghanistan.
The program was so successful that Barack Obama not only continued to authorise covert killings by drone, he quadrupled the number. The reason is perfectly understandable. America has exhausted itself in conventional war, but has not exhausted its enemies. The superpower is frustrated that it has spent more than a trillion dollars and the lives of thousands of its troops in a decade of fighting, yet the extremists continue to regenerate and regroup.
Drones deliver death without the need for forces on the ground in far-flung places, without the risk of injury to the operator sitting safely at his console in the US watching his targets on footage beamed from the drone-mounted cameras.
Media scrutiny is minimal; the ''kill list'' is drawn up in secret and the public only ever learns about a strike if the administration decides to tell it, or if witnesses on the ground can find their way into the media after the event. And, until last week, congressional oversight had been tokenistic.
The drone has become central to the American way of war despite what the chair of the US Senate intelligence committee, Dianne Feinstein, calls ''escalating ramifications''.
The New York Times' David Sanger wrote this summary: ''Today the Air Force has more drone pilots in training than pilots for fighters and bombers combined,'' he said. ''All told, at least 60 military and CIA bases, including the bases from which pilots operate upwards of four hundred Predators and Reapers, make up the vast expanse of the drone program. And a decade ago, almost none of that existed.''
The US flies drones from dozens of bases outside America. Australia's Defence Department has committed to lengthening the old runway on the Cocos Islands to allow US drones to conduct surveillance across the Indian and Pacific oceans, for instance.
And it's just a beginning. Military spending on drones is the fastest-growing part of the world aerospace industry, according to a report by the Teal Group in the US.
According to its 2011 study, global spending on drones will double in the decade ahead, reaching $US94 billion ($91 billion).
With the drone-borne death of US citizens, the US has started to examine some of the nagging doubts about the costs of the program. Is it as low-cost and high-return as it appears?
First is its morality. The US outlawed the use of assassinations many years ago. How is a drone strike any different? And what assurance is there that only the guilty are killed?
The New America Foundation, a US think tank that keeps a database of drone strikes in Pakistan, estimates 17 per cent of victims are innocent civilians or non-combatants.
Second is its effectiveness, especially when it kills the innocent.
''Dear Obama,'' wrote a Yemeni lawyer on Twitter, ''when a US drone missile kills a child in Yemen, the father will go to war with you, guaranteed. Nothing to do with al-Qaeda.''
Yemeni activist Ibrahim Mothana wrote in The New York Times that ''drone strikes are causing more and more Yemenis to hate America and join radical militants; they are not driven by ideology but rather by a sense of revenge and despair.''
How does a president weigh the tactical victory of killing individual terrorists - and the inevitable ''collateral damage'' of dead civilians - against the strategic loss of the political goodwill of entire populations?
Third is the potential for the technology to rebound. The US is not the only country to see the potential of drones. ''We are well ahead in having established systems actively in use,'' retired Lieutenant-General David Deptula, the former deputy chief of staff for Air Force intelligence, told The Washington Post.
''But the capability of other countries will do nothing but grow.''
All told, 75 countries have, or are on the verge of having, military drones. Most are for surveillance only, but have the potential for carrying arms. And, of course, the terrorists are not interested in remaining passive targets.
The laptop of a captured militant in Iraq showed that, using a $30 piece of software, he had intercepted live video feeds from US drones.
The man who has been running Obama's drone program and has been nominated as his CIA director, John Brennan, said last year that the White House was ''very mindful that, as our nation uses this technology, we are establishing precedents that other nations may follow''.
Is the US setting the best possible precedent?
Peter Hartcher is the international editor.