Sentence:  Sandman said : `` The announcement that Sen. Clifford Case R-N. J. , has decided to spend all his available time <WSD>campaigning</WSD> for Mr. Mitchell is a dead giveaway . 
Meaning of the word marked with <WSD> tags:  exert oneself continuously, vigorously, or obtrusively to gain an end or engage in a crusade for a certain cause or person; be an advocate for