There is a mindset here that treats Israel not simply as an ally but as unique among all allies in being able to dictate to the US what its foreign policy will be.
Israel is unique among all other allies, but it's not unique in dictating policy: that is an effect, not a cause. It's unique in that it plays a major role in the Pre-Millennial Dispensationalist thinking that underlies the recent Rapture talk and the Left Behind series. A rather large segment of the American public are evangelicals; a rather large percentage of those believe in an odd pastiche of 'prophecies' about the end times gleaned from Ezekiel and Revelations that purports to describe Christ's second coming. In this narrative, several events must occur before Jesus can return, and among them is the reestablishment of the land of Israel and the increase of its borders to well beyond the 1967 demarcation.
There all also other Biblical verses that those 'literally' minded like to quote: those who bless you, I will bless, those who curse you I will curse, says the Lord, referring to Israel. (Strangely they leave out the ones about how Israel would get thrown out of the land if they failed to follow the law, which included rather strict provision for the treatment of 'aliens among you'.)
The main reason for American's unconditional support for Israel, however, is that in the 'prophetic' schema held to by so many Americans, Israel's well-being and territorial expansion (including all of Jerusalem and the rebuilding of the temple there) are necessary prerequisites to the return of Christ. Any analysis of Israel-US relations must address that point.
How we address the point that American foreign policy has been developed in deference to those actively seeking to bring about the end of the world is another matter ...