What accounts for variation in the electoral success of niche parties? Although institutional and sociological explanations of single-issue party strength have been dominant, they tend to remove parties from the analysis. In this article, I argue that the behavior of mainstream parties influences the electoral fortunes of the new, niche party actors. In contrast to standard spatial theories, my theory recognizes that party tactics work by altering the salience and ownership of issues for political competition, not just party issue positions. It follows that niche party support can be shaped by both proximal and non-proximal competitors. Analysis of green and radical right party vote in 17 Western European countries from 1970 to 2000 confirms that mainstream party strategies matter; the modified spatial theory accounts for the failure and success of niche parties across countries and over time better than institutional, sociological, and even standard spatial explanations.
