This study introduces a measure of framing distance, capturing the degree of frame overlap among parties. Additionally, it provides a causal mechanism explaining differences between parties in framing distance. Parties within PR systems have to take coalition considerations in their stride, and therefore mainstream opposition parties, which have previously governed, are unlikely to adopt large framing distances. Alternatively, challenger parties, those that have never governed, are likely to frame important issues differently. Nonetheless, challengers are expected to reduce their framing distance when performing well in election polls. Electoral success acts as a trigger for these parties to reconsider their goals (policy, office, or votes) and to become more office-seeking. These theoretical propositions are confirmed on the basis of the European integration issue, using a mixed methods approach. Pooled time-series regressions on party manifestos issued by 21 parties between 1987 and 2006 in three political systems (Germany, Netherlands, and UK) are complemented with case study analysis.