Sentence:  What they have objected to <WSD>is</WSD> the attempt of the Russians to make use of the tragedy of Dag Hammarskjold 's death to turn the entire U. N. staff from the Secretary down into political agents of the respective countries from which they come . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)