Sentence:  If Mr. Kennan is sometimes a little somber in his appraisals , if his analysis of how Western diplomacy met the challenge of an era of great wars and social revolutions <WSD>is</WSD> often critical and pessimistic - well , the record itself is not too encouraging . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)