It's not so much the debate. It's the night after the debates.

These moments played a role in the two candidates’ discovery and decline. The debate, however, was not the main driver of opinion change. The way the news media frames debate moments can lead to changes in the polls for candidates. Increasingly, social media amplifies this effect and speeds the process. Once the polls move, a cycle starts that results in more news coverage of a candidate’s gains at the polls, which can then result in even more gains.

What stops most candidates’ post-debate surge is a combination of reality and the heightened focus of media attention, which moves from narratives about an unexpected success or an increase at the polls to scrutiny of the candidate. The focus on a surging candidate may simply bring to light the underlying weaknesses of a candidacy.

Usually, only candidates who are already well known can avoid the decline that scrutiny brings.