Watch the presidential debate live on ABC tonight at 9 p.m. ET.
Answer: Maybe — but not always, and when so, more indirectly than directly.
We at ABC News will be looking for answers starting with one of our patented instant debate-reaction polls tonight; more on that below. First, though, a bit of background.
Debates have been held in eight presidential contests since 1960. We find just one after which the lead changed hands by a meaningful margin: In 1980, when Ronald Reagan uttered his "Are you better off?" line. He gained seven points in a post-debate poll.
There are other cases in which debates (or post-debate evaluations) may have had a subtler, less measurable effect on the dynamics of the race. They are, after all, an essential window on the candidates' styles. After Richard Nixon's pasty-faced performance in the 1960 debates, John F. Kennedy went from 46 percent support to 49 percent; Nixon slid from 47 percent to 45 percent.
Those changes are not large enough to be significant given polling tolerances (as we're fond of saying, this ain't laser surgery). Nonetheless, collective memory maintains that the debates spelled Nixon's narrow defeat (that, or Richard Daley).
Nor did polls show significant movement immediately after the 1976 debate in which Gerald Ford said Poland was free (and news reports pounced on the misstatement); Jimmy Carter gained a single point, Ford lost three. Again, though, the gaffe may have had the more subtle effect of halting what had been a slide in Carter's advantage.
Our polls in 2000 showed no significant movement around the debates. Ditto for 1996. In 1992 there was more movement, though never enough to change the lead: Ross Perot gained 11 points through the three debates, moving from a distant third place to a still-distant third place. Bill Clinton and the first President Bush popped up and down by five or six points, possibly accommodating the Perot movement.
| 
