The purpose of this article is to analyze, using the example of Franz Mehring, the growing cleavage between German left-liberalism and social democracy in the 1880s. Due in part to the radicalization produced by Bismarck's anti-socialist law of 1878 to 1890, Marxism was firmly established within the German socialist movement in the 1880s. The reverse of that process, the growing ideological and political rigidity of left-liberalism, is less well treated. In this article, I will outline the program of social reform proposed by the then left-liberal journalist, Franz Mehring, to German liberalism in an effort to build a coalition of middle-class and working-class democratic forces in Imperial Germany. Mehring's failure was instructive both for his own intellectual and political development and for what it tells us about the relationship between social democracy and liberalism in Germany.