Increasingly, new challenger parties have emerged across European democracies, meaning established parties must determine how to effectively campaign against them in elections. The newcomers often poach established parties’ previously loyal supporters, leaving politicians within these parties wondering what messages work against the outsiders. Should they adopt the messaging of challengers, accommodating them? Should they put forward a unified face in opposition to the upstarts? Or should they orchestrate a campaign whereby the party takes on vague or varying positions, trying to be all things to all people? Using survey vignette experiments, we examine how voters react to strategies that a party they support might take in response to the rise of a hypothetical challenger party. Our findings show that while, on average, voters prefer when their parties offer a unified response to challengers, their support for their party’s approach depends on their own policy stance on this issue that challenger is attempting to compete on. In some instances, when groups of party supporters prefer the policy stance of the challenger, the established party may be better off expressing dissent or ignoring the challenger entirely. The results highlight that when established parties face new challengers, they must walk an increasingly precarious tightrope, balancing the need for unity with some degree of tolerance for dissent. They also help to explain why mainstream parties accommodate the position of challengers, despite recent evidence in political science literature that doing so can be electorally detrimental.