Sentence:  There his vote , along with those of Chairman Howard Smith , the courtly Virginia judge , and the four Republican members , could and often did produce a 6 - 6 deadlock that <WSD>blocked</WSD> far-out , Democratic-sponsored welfare legislation ( a tactic often acceptable to the Rayburn-Johnson congressional leadership to avoid embarrassing votes ) . 
Meaning of the word marked with <WSD> tags:  hinder or prevent the progress or accomplishment of