Israel would never go right ahead on their own without 1.)getting the green light from us or 2.)having us somehow directly support them in someway. And I also seriously suspect that we would never allow Iran to get a bomb if they actually are going towards that end goal.and B) convinced that our government isn't going to do squat about it, and can't be trusted to defend them. They may not, but it is hardly implausible or even at this point perhaps unlikely. They have already launched several lower level attacks against the Iranian nuclear program, some with us, and some on their own.