It is commonplace to see political parties as fundamentally constrained by public opinion. By contrast, this paper argues that party competition amplifies mass ideological polarization over public policy. Specifically, the investigation concerns the relationship between mass-level ideology and ethnic exclusionism (the call for harsh immigration policies). As party competition intensifies, this relationship strengthens. The party competition thesis is tested by performing a comparative study of Denmark and Sweden. Unlike their Danish counterparts, Swedish political parties have, most of the time, refused to take opposed stands on immigration policy. In effect, the empirical data show that the individual-level association between self-reported ideology and ethnic exclusionism is considerably stronger in Denmark than in Sweden. To investigate the party competition effect in depth, both longitudinal analyses and a cross-sectional analysis are performed. Data cover the period 1990-2008.