Sentence:  This <WSD>is</WSD> puzzling to an outsider conscious of the classic tradition of liberalism , because it is clear that these Democrats who are left-of-center are at opposite poles from the liberal Jefferson , who held that the best government was the least government . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)