Trump on respecting the election result: “I will look at it at the time.” Photo: Win McNamee/Getty Images

Hillary Clinton has used all three presidential debates to make the case that Donald Trump is unfit for office. Trump has proven himself unable to recognize this strategy, or to learn from his failures, or to change his behavior in any way. All three followed the same pattern. Trump began the debate by projecting something approximate to a normal Republican — which is to say, an angry reactionary within normal bounds.

Then Clinton began to prod and bait him, and as the evening unspooled, he progressively lost his composure. She said that Trump “choked” during his meeting with Mexican officials, and that he employed undocumented workers and refused to pay them promised wages, as he often does. Clinton’s prods, like jabs to a boxer, had a cumulative effect, swelling his wounded ego.

Trump relied in the first half of the debate on the method used by his running mate, which was to simply deny every controversial statement that either the moderator or his opponent mentioned. The tactic worked when Clinton noted Trump’s stated desire to expand the nuclear club, which Trump denied, insisting, “You won’t find a quote.” The quote exists, but Clinton could not summon it on the spot.

His confidence perhaps bolstered, Trump tried to use the same method again. When pressed by the moderator with his own quoted remarks boasting about his habit of committing sexual assault, a boast later corroborated by nine victims, Trump issued a blanket denial. Clinton effectively picked it apart. She mentioned that he insulted the accusers for being too ugly for him to bother assaulting. When Trump insisted he had not, she repeated his exact words: “Look at her, I don’t think so”; “Would not be my first choice.” He couldn’t even muster a defense.

The most important exchanges centered on Trump’s historically anomalous lack of fealty to the democratic system. When Clinton cited the American intelligence findings that Russia had orchestrated cyberattacks against her party and campaign, he repeatedly clung to his stance that Russia might not be to blame. “She has no idea whether it’s Russia, China, or anybody else,” he insisted, “our country has no idea.” Even as recently as a few months ago, it would have been hard to imagine a major-party candidate making excuses for attacks against his own country by a hostile foreign power.

Whatever reason Trump has, his stance is fitting. Putin is waging a global campaign to discredit the very idea of democracy. Trump has joined his cause. The debate culminated in Trump refusing to pledge that he would accept the outcome of the election — a statement of disloyalty to the American system of government without precedent since 1860, when Southern Democrats vowed to leave the union if the Republican Party prevailed.

Clinton framed his answer as a pattern of habitual sore-loser-dom, which Trump displayed in calling several Republican primaries rigged, and making the same complaint about losing a television award. (She did not mention that he did this on Election Night 2012, too.) Perhaps she put it this way because undecided voters can relate to the familiar archetype of a bully who happens to be a sore loser. The truth is much darker and more dangerous. Trump is a domestic insurrectionist against the stability of American government.