"It is the same group we faced in the south with those white crackers and the dogs and the police,"
Well...he may have been using the term "cracker" with its original meaning in mind. The term cracker itself converys a position of power for the person being called the slur. It comes from Slavery to refer to the overseer who would "crack" the whip at you to make you work faster. Wasn't used as a term to describe white folks in general.
Either way, it was an ignorant thing for Rangel to say.