It is generally assumed that widespread public confidence in the government is essential for political stability in the U.S. and other advanced capitalist democracies. This legitimacy-stability thesis implies that individuals with little confidence in the government would be particularly prone to support political protest. However, theoretical and empirical considerations suggest that this thesis must be revised to include a third, interacting factor—the preexistence of an organized protest movement: low confidence in the government is likely to translate into protest support only when such a movement is present. Using data from a 1972 national survey, only moderate associations are found between several indices of confidence in the government and support for political protest, and these associations are significantly reduced when salient structural factors (e.g., race, unemployment, community involvement) are taken into account. These results are not expected under the widely accepted, unrevised, legitimacy-stability thesis. However, consistent with a revised version of the thesis, it is found that low confidence in the government is strongly associated with protest support among those groups whose interests were being actively promoted by visible protest movements.