Israel does not need the US to counter attack. Israel has the world's sixth largest arsenal of nuclear weapons, behind only the US, Russia, China, the UK and (maybe) France. It can handle ANY Iranian threat on its own, thank you very much.
The U.S. estimates Israel has about 200 nuclear weapons made up of five different classes of weapons. Israel assembled its first two bombs on the night of Nov. 2, 1966. In the Six-Day War, it had two weapons on alert; by the Yom Kippur War in 1973, 20 were on alert; by the Gulf War, the number had reached more than 200.
There are thermonuclear missile warheads on missiles with intercontinental (Jericho II) and intermediate (Jericho I) range, nuclear landmines, artillery shells and neutron bombs to stop assaults across their vulnerable borders, aerial bombs attached to American-made F-15's dispersed and on alert. It has a nuclear target base of nearly 100 targets, which, like the US base, is continually updated and which, like the US, can be updated in near real time. And it has an entire wing of its Air Force, the secret 2nd Wing, to manage it all.
More importantly, Israel has a second strike capability, that is, a capability of striking any enemy even if that enemy has already destroyed Tel Aviv. A single nuclear weapon might able to take out most of the Israeli population, which lives around Tel Aviv, but Israel has enough capability to deliver a society-smashing blow on Iran within hours. Iran would be triumphant, and then incapable of functioning as a society, in very short order.
Ask why the United States is allowing such a double standard in the world.