Although US intelligence has a poor record predicting WMD, if they turn out to be right this time, it would buy Israel valuable time. Electronic countermeasures and anti-ballistic missile technology are continually improving. If Israel could successfully fend off a nuclear first strike, Iran would then be faced with the prospect of imminent annihilation. If Iran can't succeed with their initial attack, they may not be able to proceed at all. Only if US intelligence is right this time...
Fear of rioting, disorder at Temple Mount prompt restrictions on Muslim worshiper (Haaretz)
from the article: U.S.: Iran halted nuclear weapons development in 2003