Schwadel, P. and Garneau, C.R.H. 2014. "An Age-Period-Cohort Analysis of Political Tolerance in the United States," The Sociological Quarterly 55(2): 421-452.
This piece limits itself to analyzing the effect of age (and period, and cohort effects) on American political tolerance for certain outgroups. The outgroups in question are sexual minorities (lumped as "homosexuals"), communists, racists, and "anti-religionists." Using some pretty sharp methods (I can't read their data tables), the authors conclude that effects are strongest for "gays and lesbians", communists, and atheists. They discuss these matters relatively in depth, and explore their effects, controlling for college education and religious nonaffiliation, arguing that both of those factors are collinear with their dependent variable. They argue that these effects are driven by time period effects - in short, that exogenous factors unrelated to the lives of individuals drive their increased political tolerance.
My Take: I'm not sure that there's any salience to testing whether people give a damn about communists.