I have a dream that one day,down in Alabama,with its vicious

I have a dream that one day,down in Alabama,with its vicious racists,with its governor having his lips dripping with the words of "interposition" and "nullification" -- one day right there in Alabama little black boys and black girls will be able to join hands with little white boys and white girls as sisters and brothers.
请问什么叫"Down in Alabama"?
两个with在句子中作什么成分,怎么翻译比较好?“with its vicious racists,with its governor
"interposition" and "nullification"的对象是什么?你是从文字里看出来的,还是根据当时的社会情况判断出来的?