...Respected U.S. foreign policy experts call for Washington to be cautious in the Middle East and warn presidents that too much support for Israel will carry serious international costs. When presidents overrule their expert advisers and take a pro-Israel position, observers attribute the move to the "Israel lobby" and credit (or blame) it for swaying the chief executive. But there is another factor to consider. As the Truman biographer David McCullough has written, Truman's support for the Jewish state was "wildly popular" throughout the United States. A Gallup poll in June 1948 showed that almost three times as many Americans "sympathized with the Jews" as "sympathized with the Arabs." That support was no flash in the pan. Widespread gentile support for Israel is one of the most potent political forces in U.S. foreign policy, and in the last 60 years, there has never been a Gallup poll showing more Americans sympathizing with the Arabs or the Palestinians than with the Israelis.

Over time, moreover, the pro-Israel sentiment in the United States has increased, especially among non-Jews. The years of the George W. Bush administration have seen support for Israel in U.S. public opinion reach the highest level ever, and it has remained there throughout Bush's two terms. The increase has occurred even as the demographic importance of Jews has diminished. In 1948, Jews constituted an estimated 3.8 percent of the U.S. population. Assuming that almost every American Jew favored a pro-Israel foreign policy that year, a little more than ten percent of U.S. supporters of Israel were of Jewish origin. By 2007, Jews were only 1.8 percent of the population of the United States, accounting at most for three percent of Israel's supporters in the United States.

These figures, dramatic as they are, also probably underestimate the true level of public support for Israel...