Obviously America has various allies around the world, but the connection to Israel seems unusually strong. It seems like no serious presidential candidate, regardless of party affiliation, dares condemn Israel. Even under the current conditions, Obama insists on defending Israel's actions.
Historically, is Israel of strategic importance to the US? What gives?
The story there begins in 1948, just before the creation of the modern state of Israel. There was a major debate in the US about whether or not the United States ought to recognize and establish diplomatic relations with the nascent Jewish state. At this time, many prominent American Jews opposed the creation of Israel, while many others supported it. In early May of 1948, Truman famously summoned George Marshall and his Special Council Clark Clifford into the Oval Office to present both sides of the issue to him. Clifford made the case for recognition of the state that would soon adopt the name Israel, and made his case in moral and historical terms, stressing that the United States had an obligation to support a Jewish state in order to provide them with safe haven from the destructive forces of worldwide antisemitism. Marshall opposed recognition of the Jewish state, arguing that a Jewish state in the middle of the Arab world would immediately cause a war to break out, and that it would be a constant source of headaches for the United States. He even told Truman that he wouldn't vote for him in the upcoming election if he recognized the Jewish state. Truman sided with Clifford.
During the Cold War, the US and USSR avoided direct conflict with one another by instead supplying a series of client states with diplomatic and military support via a series of proxy conflicts. The US sided with Israel while the USSR sided with the Arab states, particularly Nasser's Egypt. American support for Israel was in the strategic interests of the country at this point because the United States didn't want the USSR to gain too much influence in the Middle East. It was during this period that Gold Mier observed that there was a "Special Relationship" between the US and Israel.
Today, some scholars like Stephen Walt and John Mearsheimer argue that America's continued support for Israel is no longer in its strategic interests, and further argue that America supports Israel despite the Jewish state's internationally isolated status due to the influence of a powerful and highly effective lobbying apparatus that has a great deal of influence in Congress. They published a book on this topic in 2007 called "The Israel Lobby and US Foreign Policy." (Please note that I am only reporting their views, not endorsing them).