In the United States, the term "white supremacy" is historically associated with the period of Jim Crow laws, the last of which were removed in the 1960s.

Racism is an ism--that is, a set of beliefs, norms, or group practices that can be given a coherent abstract definition and description in detail.  The Nazis, KKK, and most of the alt-right rabble are indeed racists, because they assert such beliefs, and it is possible to describe systematically what they will say and do.  The old lady down the block who still refers to black Americans as "colored" isn't "racist"--even if she admits personal distaste toward blacks.  A personal preference is not an ism.