The final presidential debate lasted for 90 minutes. In that time, Hillary Clinton and Donald Trump discussed a plethora of different topics, and each had various strong and weak moments. And soon enough, we’ll get insta-polls that will tell us about viewers’ initial reactions.

But in reality, the question of who won the debate was settled in one moment in particular — when Trump refused, yet again, to say he’d accept the results of the election if Clinton won, a topic that has consumed nearly all post-debate commentary.

Moderator Chris Wallace pressed him on the topic, and Trump avowed only that he’d “look at it at the time,” because the indicators of fraud he’s “seen” were supposedly “so bad.” Pressed again, he glibly remarked, “I will keep you in suspense, okay?”

Reporters and commentators instantly — and rightly — went into a frenzy over this remarkable statement. And the vast majority of the post-debate commentary is revolving around it:

So every network I'm watching is leading with, "Will Trump admit he lost" question. — Conn Carroll (@conncarroll) October 20, 2016

Fox News panel is astounded by Trump's refusal to accept the election results. — Josh Barro (@jbarro) October 20, 2016

Tapper on Trump’s not accepting election results: “One of the most stunning things I’ve ever heard in a presidential debate ever." — Farhad Manjoo (@fmanjoo) October 20, 2016

And even some of Trump’s most fervent boosters are admitting this was a disaster for him:

He should have said he would accept the results of the election. There is no other option unless we're in a recount again. — Laura Ingraham (@IngrahamAngle) October 20, 2016

This is so consequential because even if Trump did put in a performance that was overall reasonably effective at convincing swing voters, it will now be completely drowned out by the overwhelming focus on this one moment in the post-debate commentary.

Post-election media analysis can greatly influence how people judge a debate

Back in 2004, Kim Fridkin and several co-authors at Arizona State University conducted an experiment around a debate between George W. Bush and John Kerry. They screened the debate alone for one group of people, they showed the debate plus 20 minutes of NBC commentary to another group, and they showed the debate plus commentary on CNN.com for third group.

Overall, participants who watched the debate alone, or watched it and read CNN.com commentary, were more likely to think Kerry won. But participants who watched the debate plus NBC’s analysis afterward were overwhelmingly likely to conclude Bush was the winner.

Now, this just relates to the question of who "won" the debate. Obviously, viewers can conclude that a presidential candidate won a debate without deciding to vote for him or her.

Still, it indicates that the question of who won the debate is about more than just what voters see in the debate — it can be influenced by what voters see and hear afterward.

So even if Trump wins in insta-poll reactions, that may well not last after days of discussion of how Trump might refuse to concede if Clinton wins.

What voters will hear is that Trump is dangerous and abnormal

The fact that this is the story coming out of the debate drives home the narrative that Donald Trump is not a typical candidate for president — and suggests that he is something aberrant and dangerous.

Indeed, straight news reporters Julie Pace and Lisa Lerer of the Associated Press began their debate story with the following lede:

Threatening a fundamental pillar of American democracy, Donald Trump refused to say Wednesday night that he will accept the results of next month's election if he loses to Hillary Clinton.

And post-debate commentators for media outlets of all stripes — even Fox News — are talking about how strange and unprecedented Trump’s behavior here is.

If not for that one segment, the post-debate commentary probably wouldn’t have been good for Trump — but he could at least hope that pundits would agree that he had held his own and put in his strongest performance yet.

Instead, everyone’s talking about how dangerous he is for American democracy.

Watch: How presidential debates are won and lost