In this month's Atlantic Monthly James Fallows has a long discussion of Mitt Romney's history as a debater and what it might mean in this presidential election. It's interesting throughout, but I don't agree with this:
bq. If economic trends are bad enough—or, improbably, good enough—to turn the election into a runaway, we might look back and say that the debates didn’t matter. But in what gives every sign of being a close, bitter, expensive, and mostly negative contest, the way these men interact onstage could make a major difference. Debates played an undeniable role in the victory of John F. Kennedy over Richard Nixon, in 1960; of Jimmy Carter over Gerald Ford, in 1976; of Ronald Reagan over Carter, in 1980; of Bill Clinton over George H. W. Bush, in 1992; and of George W. Bush over Al Gore, in 2000.
I would frame this point differently, and I have a new piece at the Washington Monthly that says why. My piece reviews the evidence about the impact of presidential debates. Here is one paragraph that summaries my take:
bq. That presidential debates can be “game changers” is a belief almost universally held by political pundits and strategists. Political scientists, however, aren’t so sure. Indeed, scholars who have looked most carefully at the data have found that, when it comes to shifting enough votes to decide the outcome of the election, presidential debates have rarely, if ever, mattered.
Part of that conclusion is based on the research of James Stimson, Robert Erikson and Christopher Wlezien, and Thomas Holbrook. Part of it is based on a look at each of the debates that "played an undeniable role." Even in these cases, there is generally no solid evidence that debates mattered. The polls didn't move, or the polling data are too thin to separate a debate effect from sampling error, or there were other events surrounding the debates that make it difficult to attribute movement in the polls solely to the debate. And so on.
The best starting point for any discussion of the 2012 presidential debates is this fact: in the modern era, presidential debates have very rarely decided the winner, and even when they may have done so, the evidence is too thin to make a definitive conclusion.
Again, here's my piece.