‘Will you shut up, man?’

A reader emailed me before dawn Wednesday to say that in more than 60 years of presidential debates, he had never seen anything like what happened hours earlier. Yes, it’s true, we’re still in Trump Land, Toto.

One can imagine analysis will arrive from Trump Land that blowing up the debate was Mr. Trump’s plan going in. What other than a thought-out strategy, perhaps to capture the so-called secret Trump voters, could explain the president dynamiting it from start to finish?

Conventional wisdom is that because it was a debacle, the debate didn’t change any minds. But the high percentage of committed party-line voters has been a reality for months. Other than driving turnout from a polarized electorate, these presidential debates are about winning at the margin by pulling over undecided or leaning voters.

This especially includes women, with whom Mr. Trump lately has been underwater and sinking in battleground-state polls. Here’s guessing few women migrated to the Trump column Tuesday evening.

The Biden team has had a plan for appealing to gettable voters from day one. The strategy has two prongs. First, run against Mr. Trump’s personality and character. It’s the idea that whatever you think of his policies, “Trump” with his double-dose persona has worn out his welcome in just four years.

The second, policy-based prong is to drive the perception of Mr. Trump that is freshest in the public’s mind—that he mishandled the coronavirus, the biggest public-health threat of our lifetimes. Set aside how little the reality comports with this charge. Reality is irrelevant to an opposition election strategy.

Polls have put public disapproval of Mr. Trump on the virus at nearly 57%, a high number given that most governors have strong approval ratings on the virus. This is almost entirely a function of the early, ill-run coronavirus news conferences, which consisted mainly of Mr. Trump promoting himself and picking fights with reporters, when the country was tuning in daily for straight information about the emerging crisis. If Mr. Trump loses, those press conferences will be the straw that did it.

Central to the Biden team’s strategy is their recognition that Mr. Trump’s Achilles’ heel is personal criticism. He can’t take it. Ever. His instinct to crack back is hair-trigger.

This worked for him in the 2016 GOP primary debates against Low Energy Jeb, Lyin’ Ted, Little Marco and the rest. It sort of worked because the jammed stage minimized his time on target. Though not to everyone’s taste, his primary debate performances established Mr. Trump in many voters’ minds as the Anti-Politician.

The crack-back compulsion continued with the White House press corps, and in time became less amusing. Instead of opportunities to explain his policies, the exchanges turned into tiresome, predictable cat fights. Goading Mr. Trump became a press routine, like working out at the gym.

Mr. Trump has been called, not without justification, a necessary bull in the dusty china shop of politics. But Tuesday night he looked like a bull on the floor of an arena, tiring and turning first to face picador Chris Wallace and then lurching back at Mr. Biden’s toreador. It got hard to watch.

Mr. Biden proved he isn’t Mel Brooks’s 2,000-year-old man, but he is an aging politician, unable to sustain a normal campaign and struggling to reconcile or explain his party’s abrupt drift to the edge of socialism. But with 47 years in the trenches, Mr. Biden is a political pro, which means being case-hardened against personal criticism.

The debate was 90 minutes of maybe the only thing Joe Biden is still good at—parrying attacks, whether from former presidential candidate Kamala Harris or Mr. Trump. When Mr. Trump finally played the Hunter Biden card and “cocaine use,” Mr. Biden said his son, “like a lot of people at home,” was fixing the problem—and millions of moms nodded in sympathy.

Mr. Biden ran through his talking points, however preposterous, such as suggesting cops take along a psychiatrist on 911 calls. The biggest Biden vulnerability came when he asserted, “You can’t fix the economy until you fix the Covid crisis.” Lockdowns to the horizon.

The president’s response—that people want their schools and restaurants open and that he restarted Big Ten football—was OK but not enough on an issue central to his re-election.

Mr. Trump has a good story to tell. The speakers at the impressive GOP convention created a narrative template for the campaign, but that story wasn’t told Tuesday night.

When asked to address race in the U.S., giving Mr. Trump a chance to talk about his prison releases and minority job creation, he segued into a 25-year-old anecdote about Mr. Biden and “superpredators.” Even sympathetic voters have difficulty absorbing a good political record if it’s conveyed to them in random semi-soundbites.

This first presidential debate will be remembered for five words: “Will you shut up, man?” Amazing to think that may be what turns deciding votes in this election.

Write henninger@wsj.com.