There is amazing irony in modern day leftists promoting racist theories. Before World War II, belief in white and Nordic superiority was widespread in this country. Restrictions imposed on immigrants from Asia and Eastern and Southern Europe were based on the racial "science" promoted by much of the academia and many of influencers of that day. Blacks were subject to medical experiments as they were regarded as inferior to whites. The liberals in the New Deal era and thereafter were prominent in attacking racial discrimination.
But perhaps this is a long term leftist strategy: first to take down laws and customs promoting racial discrimination; second to promote discontent among minorities; third to use angry minorities as a club against the white population and the country in general. Liberals' promotion of civil rights in the 1960s won the black and Hispanic communities to their side.
Uhh...
The Republicans, liberal and otherwise, are the ones that promoted and passed civil rights laws in the 1960s.