Many, many moons ago, my family elders advised me: “Son, prepare yourself, because you never know when the doors of opportunity are going to open up. And when they do, you need to be ready to step inside.” 

That was good advice, although I didn’t immediately take it to heart. I had to learn the hard way that walking through those doors meant cracking my books open first.

Democratic presidential candidate Kamala Harris made no mistake about the opportunity before her last Tuesday night in her televised debate with Republican opponent Donald Trump. She was a woman with a plan, and she executed it flawlessly.

Trump was another story.

While the former president is a master of the internet arts of insult and relentless trolling, in the debate he showed himself to be utterly unprepared for face-to-face competition with an opponent who had done her homework.

Harris, a former prosecutor, seemed prepared to use every tool at her disposal. She understood Trump’s deepest insecurities, and she wasted no time in coaxing her opponent to vent them.

Directly challenging Trump’s ability to keep his cool by insulting him personally is not a game for the squeamish. Yet Harris did so with startling ease. One imagines that Trump’s advisers warned him against taking the bait, but he couldn’t help himself.

The contrast between the candidates was embarrassingly apparent.

Harris cited respected academic economists to argue that Trump’s tariffs would be costly to consumers and potentially disastrous to the economy. Trump replied by citing the plaudits of Fox hosts Laura Ingraham and Sean Hannity.

Harris pointed out the large number of past Trump cabinet members who have warned that he would endanger American democracy if elected again. She revealed that numerous NATO leaders had privately expressed similar sentiments about his threat to the trans-Atlantic alliance, calling him a disgrace.

Trump retorted that Hungary’s strongman, Viktor Orban, is a major fan.

Closer to home, Harris zinged Trump—deservedly—for injecting himself into a bipartisan agreement on a border protection bill to kill it.

Which raises the question of whose side Trump really is on in the border debate. As Harris put it: “Donald Trump got on the phone and called up some folks in Congress and said, ‘Kill the bill.’ And do you know why? Because he’d prefer to run on a problem instead of fixing a problem ...”

No need to be more complicated than that. What really infuriated Trump was that he faced an opponent who gives as good as she gets in the game of toppling the self-important.

For the first time, it seemed, Trump the TV star had found something like his match in political showmanship. Perhaps no remark cut more deeply than when Harris asserted, “Donald Trump was fired by 81 million people ... and clearly he is having a very difficult time processing that.”

Unable to quite match the Harris assault, Trump made stuff up like a high school gossip. Without evidence, for example, he claimed that Biden and Harris still hold grudges against each other, and he blamed her rhetoric for the failed assassination attempt against him in Pennsylvania.

But Trump hit a new and bizarre low in common decency when he falsely declared that Haitian immigrants in Ohio were hunting and eating dogs and cats.

Even Harris seemed momentarily stunned by the absurdity of the remark, which ABC anchor David Muir pointed out had no evidence to back it up—but that didn’t stop Trump from doubling down anyway.

Two months ago, the Democratic Party had much to worry about. President Biden, then the presumptive nominee, was flagging in public opinion polls.

His disappointing performance in a televised debate added to widespread doubts about his ability to beat Trump.

Since Harris secured the nomination, the dynamics of the race have changed. Yet on Tuesday, Trump’s performance seemed to indicate that his campaign has not adapted to a new opponent.

In the debate, Harris may not have delivered all the messages that undecided voters needed to hear. She did not fully answer questions about the economy, the issue of greatest concern for the electorate this year.

However, she did something that was immediately apparent to every American watching that debate. A door of opportunity opened as she walked on stage with a smile and an outstretched hand that seemed to catch the former president by surprise.

She, by comparison, appeared to see the doors of opportunity open up—and she was prepared to walk right in.

The writer is a columnist for the Chicago Tribune.