Sentence:  The party of pro-slavery reaction was for the moment in the ascendant; and as by an irresistible impulse, the Supreme Court of the United States was swept from its hitherto impartial judicial <WSD>moorings</WSD> into the dangerous seas of polities. 
Meaning of the word marked with <WSD> tags:  Something to which one adheres, or the means that helps one to maintain a stable position and keep one's identity - moral, intellectual, political, etc.