The Obama administration�s initial ambivalence toward democratic revolutions in Tunisia and Egypt in 2011 points to a central puzzle in US foreign policy. In some countries, during some periods, America promotes liberal democracy; in other countries and periods, it tolerates or even supports authoritarianism. Why the variation? We focus on discrete decisions by a US President to retain a dictator or instead press for democracy in a client state S. Two conditions must be satisfied for a President to do the latter. (1) An exogenous domestic crisis must threaten S�s authoritarian regime. (2) The US domestic model of free-market liberal democracy must face no credible alternative in S�s region as a route to national development and security. A credible alternative model (e.g. communism or Islamism) threatens US interests by making dissenting elites in S more hostile to US hegemony and more accepting of the hegemony of America�s security rivals; that in turn makes free elections in S riskier for Washington. But when conditions (1) and (2) coincide, a new bargain emerges: S�s elites, now assenting to the US model, pledge to participate in the US-sponsored regional order, and Washington presses S�s regime into democratizing. We test our argument against two cases involving relations between the US and the Philippines, an authoritarian client until 1986. In a 1978 crisis, communism�s high credibility in Southeast Asia forced Jimmy Carter to continue supporting the Marcos dictatorship. In a 1985�86 crisis, communism�s lack of credibility allowed Ronald Reagan to drop Marcos and permit democracy.