When Can Political Parties Credibly Change Their Policies?

When can a party credibly change its policy on an issue? No institutional device forces parties to keep their promises after being elected. Voters may thus view platform shifts as mere pandering, discounting their credibility. We propose that voters use the direction of a platform shift as a signal of the party’s motives and policy commitment. Shifting to an unpopular position is a costly signal of principled motives, while a shift to a popular position suggests opportunistic motives. Two preregistered survey experiments, one using hypothetical parties and another using a real case of mainstream party accommodation to the radical right, show that voters infer party motives and commitment from platform shifts in line with the predictions of our argument. Our study provides an explanation for the electoral persistence of radical right parties, for party system change, and for why platform shifts often fail to affect voter perceptions of party positions.