Politics is not a game of myths. America's support for Israel is rooted in the fact that they can gain a lot of things from Israel. If there is nothing to gain, the US will withdraw her support without a second thought. But what are the possible benefits the US can get from this support?
1. International Support
While the US can actually stand alone and ignore the popular opinion of other countries and the international community, the United States, like every other nation, always want to present every action it takes as if it has the full support of the international community.
On this grounds, the benefits it derives from its support to Israel is unmatched. Israel is always known for its unflinching support at the UN for all US actions like the Grenada invasion or the Libya bombing of 1986 despite the obvious opposition of other strong US allies like the Great Britain.
2. Military Support
The United States expects all its allies to collaborate with its military to form a joint task force and have a coordinated military action.
Again, Israel has a very strong record here: transferring the seized Soviet technology into the United States while the Cold War lasted. This was carried out through the combined growth of military technology to the status of poster-child due to the US military technology supremacy over its Soviet equals. The US certainly relies on Israel as its base for all military actions is South-West Asia. The US has over 1 billion dollars equivalent of military device in Israel, for all its military actions in that area.
3. Intelligence Gathering Cooperation.
It is expected that all secret services of all allies should cooperate to distribute information that serve every ones common interest.
The US and Israel work very closely when it comes to gathering information. Most of such information are classified information, of course, but from the little material made available to the public, we gathered that the US benefited mostly from the information obtained Israel GSS on the secret speech of Nikita Khrushchev in 1957 denouncing Stalin.
4. Economic Relations
The first ever free trade agreement entered into by the United States was between the US and Israel which facilitated a number of trade agreements between the two powerful nations. About $15 Billion is exported to Israel by the US.
But, leverage remains the most probably benefit the US derives from the relation with Israel. Suffice it to say that, it is all about making Israel agree with whatever the US wants, such as the ability to stop Israel from selling arms to countries like India and China, like the ability to make Israel agree to take part in the Madrid Conference, as well as not participating in the first Iraqi war.