As a side light to the Clinton-Obama confrontation, everyone’s asking if someone from the second tier can break through tonight. Historically, you need a big issue to do that-McGovern did it with the Vietnam war in 1972; Gephardt broke into the top tier in 1988 running on the issue of foreign trade. A breakthrough has to be powered by an idea- or maybe by the stylistic performance of the century. What the second tier has to do is to make a good impression that outlasts the night, get noticed, inch up, and begin raising some more money.
By the way, the focus on Clinton and Obama also ignores the reality, in my view, that John Edwards is and will be in the first tier because of his strength in Iowa, Nevada, and maybe New Hampshire. For him and for the ultimate outcome the national polls matter a lot less than where the candidates stand in those early states.