Besieged by insurgencies in Afghanistan and Iraq and gripped by mounting pressure to enhance security and public safety at home, officials in Washington and Ottawa are now confronted with a serious homeland security dilemma: the greater the financial costs, public sacrifice and political capital invested in security, the higher the public's expectations and corresponding standards for measuring performance, the more significant the public's sense of insecurity after each failure, and, paradoxically, the higher the pressure on governments and citizens to sacrifice even more to achieve perfect security. The paradox of security dilemmas at the international level (Jervis, 1976, 1978) explains why perfectly rational decisions to enhance power actually diminish security by promoting unstable spirals in competitive defence spending--a common account of escalating military budgets throughout much of the Cold War. The homeland security dilemma represents the post-9/l I equivalent for domestic politics in the war on terrorism. The paper's central argument can be summed up by the following counterintuitive thesis: the more security you have, the more security you will need, not because enhancing security makes terrorism more likely (although the incentive for terrorists to attack may increase as extremists feel duty bound to demonstrate their ongoing relevance), but because enormous investments in security inevitably raise public expectations and amplify public out-rage after subsequent failures. [ABSTRACT FROM AUTHOR]