Sentence:  In each of the last , the trial marked the beginning of a new course : in Moscow the liquidation of the Old Bolsheviks and the tightening of Stalin 's dictatorship ; in the United States the initiation of militant anti Communism , with the repentant ex Communist in the <WSD>vanguard</WSD> . 
Meaning of the word marked with <WSD> tags:  the leading units moving at the head of an army