Sentence:  As Chairman of the relevant committee, Yarborough would ordinarily have been the bill's <WSD>Floor Manager</WSD> during the Senate debate; Magnuson might indeed have replaced him, but ironically, Magnuson had not yet returned from a weekend trip to Seattle. 
Meaning of the word marked with <WSD> tags:  One who manages the floor of a (dance), (club), or other gathering of people.