Sentence:  To my knowledge , Lincoln remains the only Head of State and Commander-in-Chief who , while fighting a fearful war whose issue <WSD>was</WSD> in doubt , proved man enough to say this publicly - to give his foe the benefit of the fact that in all human truth there is some error , and in all our error , some truth . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)