Sentence:  The wrong man in the wrong position , perhaps even in a junior position abroad , can <WSD>be</WSD> a source of great harm to our policy ; the attitudes of a U.N. delegate who experiences difficulty in finding adequate housing in New York City , or of a foreign diplomat in similar circumstances in our Capital , can be easily be directed against the United States and all that it stands for . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)