Our politicians' support for Israel is based on several things, not the least of which is appeasing Jewish and certain Evangelical voters—sources of votes and campaign contributions. The belief that Israel was the birthplace and home of Jesus is an integral part of the support by many of the religious.
Another reason for support of Israel is the belief that Israel provides a bastion for the US in the Middle East. This belief is unfounded, because Israel has always and will always do what is best for Israel, not the US.
Another is residual guilt for the Holocaust, the MV Stuma, and especially the MS St. Louis, which after being denied entry into the US in 1939, returned Jewish refugees to Europe where about 250 of them later died in concentration camps.
Another is the arms trade between the US and Israel. I don't know the balance of payments, but Israel buys a lot of US weapons. On the other hand, the US provides Israel a lot of aid money to buy those weapons.
Hidden in the arms trade is the benefit that Israel provides "live fire testing" for these weapons, something the US isn’t always able to do.
I suspect a very close relationship between Rafael Advanced Defense Systems, an Israel research and development (R&D) company, partly responsible for the Iron Dome anti missile system and US arms manufacturers.
The US shared the cost of R&D of Iron Dome, and co-produced the older Arrow III missile system, about half of which was built by Boeing. At the least, the US and Israel almost certainly share technology.
While Israel may provide the US some intelligence, the larger and broader US intelligence assets and sources almost certainly provide more information to Israel than they to us.
You may have seen the announcement that Israel accepted delivery of two F-35 fighters o/a 12 December 2016. The jets are built by US's Lockheed, and are the first of 50 to be delivered to Israel. It's likely that they will be "combat-tested" before any that are in the hands of US units.
Another reason for support of Israel is simply habit, and our inability to re-examine the fundamentals and consider that our thinking may have been, or may now be, wrong.
I would clarify "habit" to mean that many people in this country are blinded by perceptual filters. They have, perhaps for one of the reasons I've mentioned above, created a belief in their mind that "Israel is an ally and must be supported." As we humans do with all such beliefs, they then built a wall around that belief. Any information that supports the belief passes easily through the wall and strengthens the belief and the wall. Any information that contradicts the belief is not only rebuffed by the wall, but serves to make the wall stronger.
It is not usually possible to break down such walls by a frontal attack, but only by undermining them. Think Henry V and the siege of Harfleur as transmogrified in the Kenneth Branagh production (historically inaccurate, but almost certainly better than history). In the Branagh movie, if I recall correctly, the walls of Harfleur were broken by sappers tunneling below them.
We may be able break down such walls in our own minds by following the advice of Peter Abelard:
• Doubt; question everything. Doubt leads to questioning; questioning leads to truth.
• Distinguish rational proof from propaganda or persuasion.
• Be precise with words and demand precision of others.
• Be wary of error, even in the most sacred texts.
Registered Curmudgeon, scientist, skeptic, humanist, and writer.