When Prime Minister Ariel Sharon first proposed his Gaza Disengagement Plan he did not seek a quid pro quo from the Palestinian side. Instead, he obtained one from the United States in the form of a letter from President George W. Bush, dated April 14, 2004, in which the U.S. assured Israel that with respect to the disputed West Bank, Israel was entitled to defensible borders. How the idea of defensible borders works into the post-Iraq War Middle East is fully examined as well as the territorial, legal, and policy implications of this critical U.S. guarantee.