This study tests two sets of competing hypotheses about the relationship between trait reactivity to positive and negative stimuli (i.e., motivational reactivity), moral stances on social principles (i.e., social morality), and political ideology. The classic view contends that a specific political ideology or social morality results from a specific motivational reactivity pattern, whereas the dynamic coordination account suggests that trait motivational reactivity modulates an individual's political ideology and social morality as a result of the majority political beliefs in their immediate social context. A survey using subjects recruited from a liberal-leaning social context was conducted to test these hypotheses. Results support the dynamic coordination account. Reactivity to negativity (indexed by defensive system activation scores) is associated with the adoption of the dominant social morality and political ideology. Reactivity to positivity (indexed by appetitive system activation scores) is associated with the adoption of nondominant social moral and political stances.