As to timing, Mr Perkovich explains how India was yanked across the nuclear threshold for crude party-political reasons.

ECONOMIST: India

Anti-nuclear types argue this kind of activity "lowers the nuclear threshold, " making the use of such weapons more likely.

CENTERFORSECURITYPOLICY: Center For Security Policy

Previous governments have tip-toed close to the nuclear threshold, but pulled back for fear of the high price India would pay for breaking the nuclear taboo.

ECONOMIST: A waste of nationalist pride

The report which was submitted to French President Nicolas Sarkozy late last month concluded that unless something changes, Iran will have passed the nuclear threshold by the end of 2009 and will become a nuclear power no later than 2011.

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Obama doesn't want to be the U.S. president on whose watch Iran crossed the nuclear weapons threshold and certainly neither does Bibi want to be the Israeli prime minister held responsible.

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This gives rise to the worry that the distinction between conventional and nuclear warfare would be blurred, leading to a lower threshold for a nuclear attack, and thus to the undermining of the global non-proliferation regime.

ECONOMIST: America’s new posture | The

There is still some doubt how comprehensive this treaty will be, since some of the nuclear-weapons states hold out for permitting a threshold of small explosions (equal to 500 tons of TNT or less).

CNN: ASIANOW - Asiaweek

At the summit, the United States will sign accords on enhanced verification procedures sought by the Reagan Administration for the Threshold Test Ban Treaty and the Peaceful Nuclear Explosions Treaty of the 1970s as prerequisites to ratification by the U.S. Congress.

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According to Brahma Chellaney, a noted expert on nuclear and security issues at the Center for Policy Research in Delhi, "threshold" is not a technical term but an expression coined by analysts to describe countries that have successfully conducted weapons tests but have not declared themselves to be nuclear states.

CNN: OUT OF THE CLOSET