At times during tonight’s debate, Donald Trump seemed controlled, succinct, even prepared.

It didn’t matter. In an instant, he lost the debate and blew his chance of using it to turn around his sinking campaign.

That instant came when Trump refused to say he would respect the outcome of next month’s vote.

Barring some massive unforeseen news, that comment will dominate political conversation in the coming days. By next week, it will be all anyone remembers about tonight. And for good reason. A major party nominee suggesting he won’t concede defeat in a presidential election he has clearly lost was, until Trump came along, unthinkable. Had Al Gore taken that position in 2000, the United States might not be a functioning democracy today. If Trump’s position becomes the new normal--if future candidates refuse to respect the voters’ will--America may not remain one. Democracies require public legitimacy for their survival. When powerful actors withhold that legitimacy, the system crumbles.

The good news is that Trump’s answer will devastate him politically—perhaps even more than the groping scandals. It will devastate him because the minute the debate ends, journalists will begin asking every Republican they can find whether they agree that he doesn’t need to concede defeat. And many of those Republicans—including the ones on Trump’s own campaign—will feed him to the wolves.