A term used to define a person that makes decisions on the basis of race. Race is a construction built to subvert races to the benefit of one race (guess which one? Hint: they are not the majority in the world). While bigotry is possible with anyone of any race, a racist is a person who belongs to the racial group in power. So while anyone can claim Native American heritage, whether true or not, racists have the unrecognized ability to mask their privilege and go through life without having to examine oneself. Not everyone is racist, but those who never question their privilege are enjoying the benefits of whiteness.
The racist attitudes of the posters shifted the blame to the marginalized group, in effect avoiding the issue completely. By the way, "crackers" was a result of the ones "cracking" the whip.