POLL WATCH: The difficult task facing Emerson and other Clinton operatives nationwide was illustrated by a recent Gallup Poll. The survey found that among political independents--a group that often decides the outcome of close elections--Clinton's support stood at just 16%. . . . By contrast, a Gallup Poll in June, 1988, found soon-to-be Democratic nominee Michael S. Dukakis the choice of 43% of independents. In the recent poll, Perot was backed by 52% of the independents, President Bush by 21%.