They're saying that some of the people in powerful positions are racists who burn crosses. Burning crosses is a KKK harassment activity where they erect and burn a cross on the lawn of a black person's home while wearing masks to hide their true identity. Essentially they're alluding to systemic racism.
I can't find a source for this at the moment, but I read somewhere that the original line was "Some of those that hold office/are the same that burn crosses." It rhymes a lot better.