Amid mounting tensions over whether Israel will carry out a military strike against Iran's nuclear program, the United States and Israel remain at odds over a fundamental question: whether Iran's crucial nuclear facilities are about to become impregnable.
Israel's defence minister, Ehud Barak, coined the phrase "zone of immunity" to define the circumstances under which Israel would judge it could no longer hold off from an attack because Iran's effort to produce a bomb would be invulnerable to any strike. But judging when that moment will arrive has set off an intense debate with the Obama administration, whose officials counter that there are other ways to make Iran vulnerable.
The difference of opinion over Iran's nuclear "immunity" is critical because it plays into not just the timing about a possible military strike, but the calculations about how deeply and quickly sanctions against Iran must bite. If the Israeli argument is right, the question of how fast Iran can assemble a weapon becomes less important than whether there is way to stop them.