Voices of the party base: How supporters want established parties to respond to new parties

New parties have emerged across European democracies, forcing established parties to develop strategies to campaign against them. But how do supporters want their established parties to respond to these new parties? Using survey experiments in 14 European countries, we examine how party supporters react to responses their preferred parties might take to the rise of a hypothetical new party. Our results primarily highlight that voters care about substantive representation. They endorse accommodative responses towards a new party offering a policy they agree with. Thus, the extent to which party responses bind supporters to established parties is highly contingent on the distribution of policy positions among their supporters. Often, established parties must walk a precarious tightrope, balancing the need for unity with some degree of tolerance for dissent. Hence, our results explain why parties accommodate the position of new parties, despite recent evidence that doing so can be electorally detrimental.