When do voters punish mainstream party accommodation of Eurosceptic and anti-immigration parties?

When does mainstream party accommodation of niche challengers fail? Previous research demonstrates that voters often electorally punish mainstream parties that shift towards more Eurosceptic and anti-immigration positions. Current explanations focus on niche party legitimization but fail to explain why some mainstream parties fare better than others. I argue that the missing puzzle piece may be found inside the accommodating mainstream parties. Drawing on literature concerning the consequences of intra-party divisions, I theorize that voters are more likely to punish divided mainstream accommodators, as they generally regard them as less competent, as well as less credible, and are less likely to be persuaded by their mixed messaging. Consequently, moderate voters are more likely to back other mainstream competitors, whereas voters who sympathize with the niche party’s positions opt for "the original". To test these theoretical propositions, I examine voting behavior in over 30 national and 3 European elections from 10 Western European countries between 2002 and 2021. I utilize data from national election studies, election manifestos, expert surveys, and candidate surveys, covering issue competition on immigration and European integration. The paper contributes to our understanding of how party strategies and intra-party dynamics shape voting behavior and sheds light on when and why voters reject mainstream accommodation attempts even when parties shift closer to their preferences.