"Anything short of a categorical, even vociferous U.S. refusal to countenance an Israeli attack (on Iran) might have horrific consequences.."

Via TomDispatch, here

"....a longstanding Israeli strategic principle: that no neighboring state or combination of states can ever be allowed to achieve anything faintly approaching military parity, because if they do, they will try to destroy the Jewish state. By this logic, Israel's only option is to establish and then maintain absolute military superiority over its neighbors; they will, so this view goes, accept Israel's presence only if they know they're sure to be defeated, or at least vastly outmatched....Recent developments in Israel could certainly give the impression of a nation preparing for war: the Home Front command, one of four regional divisions of the Israeli army, has just announced the largest defense exercise in the country's history..... Any U.S. rapprochement with Iran -- especially if carried out on terms that acknowledge Iran's status as a regional power -- could, they fear, undermine Israel's "special relationship" with Washington...

Washington could work out a grand bargain with Tehran terminating its policy of regime change and ending sanctions in return for Tehran's vow never to weaponize its nuclear program. Intrusive international inspections would presumably guarantee such a bargain, but Tehran's national pride would remain intact, as it would be allowed to retain the right to enrich uranium and develop a peaceful nuclear infrastructure. To Israel, this would be a completely unsatisfactory compromise.....

Given the Netanyahu government's visible determination to attack, an ambiguous signal from Washington, something far less than a green light, could be misread in Tel Aviv. Anything short of a categorical, even vociferous U.S. refusal to countenance an Israeli attack might have horrific consequences. So here's a message to Obama from an observer in Israel: Don't flash the yellow light -- not even once."