Do presidential debates usually matter? Political scientists say no.

The first of three debates between President Obama and Mitt Romney airs tomorrow. History is littered with examples of debate performances that allegedly decided elections. …

But did any of those actually matter? The best political science says no.

Perhaps the most compelling evidence for the irrelevance of debates is that polling in past races hasn’t changed much at all following them. [cont.]

Dylan Matthews, Washington Post

Presidential trial heats: