Sentence:  If an intelligent stranger desired to discover the root of our national difficulties, he would naturally inquire into the history, character, and action of the political parties into which our people have been divided. ... he would learn the history of a party of perpetual opposition, constantly vilifying the administration of Jefferson, Madison, Monroe, Jackson, and of the later Democratic Presidents, <WSD>chameleonizing</WSD> itself as often as its inflexible purpose of opposition required. 
Meaning of the word marked with <WSD> tags:  To transform oneself, as if changing colour like a chameleon.