You also have to look at what support you would get from the US if things go badly in an attack on Iran. The people in the US are fed up with wars. We want nothing to do with more wars. What happens if you start a war? Will the American people go along with it or protest it? In an election year, you had best take that into consideration because politicians will cave in during an election year to organized protests to war.
from the article: Israel has responsibilities as a U.S. ally