A good debate performance probably won't do much. A bad performance certainly will hurt in most cases.
A lot of us remember algore's plastic mannequin makeup and his heavy sighing costing him.
We also remember Reagan's "There you go again" helping him.
All said and done, most debates aren't even debates. Usually the candidates repeat, ad nauseum, their stock talking points regardless of the question. IMO most debates are beauty contests for the moderators. They are pushing their images more than the issues. The PBS presstitutes are the worst at that.
That's not what cost him the race. Respectfully disagree.
AlGore was a horrible candidate to begin with.
Reagan beat Mondale in a 49 - 1 rout, never before seen in history.
"There you go again" was hardly responsible for that. Reagan was already immensely popular and Mondale telling an entire country he'd raise their federal income taxes by a lot is what doomed his campaign.
The Reagan Recovery was well under way, Reagan's popularity and likeability is what won the day, not "there you go again."
How about:
"I am not going to exploit, for political purposes, my opponent's youth and inexperience."