[theold]

The US cannot afford to have a land war with Iran. The latter is about 4 times the size of Iraq and 75 times the size of Israel. What they can do is to allow Israel to bomb here and there, shared intelligence. Then it is their turn to bomb here and there if Israel cannot make it. 

Israel's capability is limited as Iran is out of their scope. They have to fly over Jordan and over Iraq to reach Iran.