Outside of the Nixon-Kennedy 1960 debates, the 2000 Gore-Bush debate is the only one that showed a drastic shift from one candidate to another.
"Across the entire 2000 debate period, the race shifted from an 8-point lead for Gore to a 4-point lead for Bush," according to Gallup Poll analyst Lydia Saad.
Gallup research condcuted during the 2008 election supports this view stating that "presidential debates are rarely game changers" and noting only a "few instances in which the debates may have had a substantive impact on election outcomes."
Despite research, Romney remains optimistic about all three debates.
“It'll be conversation with the American people that will span almost an entire month," Romney said in Denver last night. "We'll describe our respective views, and I believe the people of Colorado will choose a better way forward for our country."
The first debate will take place tomorrow night at the University of Denver.