Illiberal democracies gain legitimacy, and thus strength, from the fact that they are reasonably democratic. Conversely, the gravest danger that illiberal democracy poses - other than to its own people - is that it will discredit liberal democracy itself, casting a shadow on democratic governance. This would not be unprecedented. Every wave of democracy has been followed by setbacks in which the system was seen as inadequate and new alternatives were sought by ambitious leaders and restless masses. Today, in the face of a spreading virus of illiberalism, the most useful role that the international community, and most important the US, can play is to consolidate democracy where it has taken root and to encourage the gradual development of constitutional liberalism across the globe.