By any reasonable standard, Vice President Kamala Harris soundly defeated former President Donald Trump during Tuesday night’s presidential debate.

She did this by demonstrating a superior understanding not only of policy but also of her opponent’s psychology. Harris figured out exactly how to anger Trump, how to trick him into changing course, and how to keep the debate on favorable ground.

To put it more bluntly, Harris manipulated Trump into a downward spiral at several points during their first (only?) debate.

Let me give you an example. Early in the debate, the moderators pressed Harris on President Joe Biden’s unpopular immigration record, asking her if she would have done anything differently than her current boss — a topic that was favorable to Trump.

Harris answered the question, but then launched into a seemingly unrelated attack on Trump’s rallies.

“I’m going to invite you to attend one of Donald Trump’s rallies because it’s really interesting to watch. You’ll see that at his rallies he’ll talk about fictional characters like Hannibal Lecter. He’ll talk about (how) windmills cause cancer. And what you’ll also notice is that people leave his rallies early out of exhaustion and boredom,” the vice president said.

This gave Trump a choice: prosecute Harris on immigration, an issue she is weak on, or go on a tirade defending his vaunted rallies. You can guess what he chose.

“Let me respond to the rallies,” Trump said. “She said people are leaving. People are not going to her rallies. There’s no reason to go. And the people that are going, she busses them and pays them to be there.”

That was the beginning of a downward spiral: a series of strange sidetracks, including a humiliating tirade about the completely fake problem of Haitian migrants supposedly eating dogs in Springfield, Ohio, punctuated by immense concern about the honor of Trump’s rallies. He never really got back to what he should have been doing: attacking Harris on migration across the southern border.

By poking Trump in the sore spot, namely at the meetings he considers so important, Harris managed to throw him off balance. To be honest, he never fully recovered from that.

Harris used this strategy over and over again.

During a discussion about crime, Harris brought up Trump’s own conviction, prompting him to launch into a tirade about “political prosecutions” instead of effectively pushing Harris on her turn on crime policy.

She broached world leaders who called him a “disgrace,” and forced him to brag about his relationship with Hungarian “strongman” (in Trump’s words) Viktor Orbán, perhaps not a criticism that the swing voters of Michigan, Wisconsin or Pennsylvania were clamoring for. She poked fun at his close relationship with Russia’s Vladimir Putin, and criticized “what you think is a friendship” with a “dictator who would eat you for lunch.”

Trump kept snapping, losing control of his temper and going in the wrong direction, while Harris watched with a smile on his face.

In retrospect, this strategy may seem innovative, but it says something about Trump’s psychology.

When discussing foreign policy during the Trump years, I often heard national security professionals express the fear that Trump was easy to manipulate: His well-known vanity and narcissism made it easy for foreign powers to extract political favors through personal flattery and lavish receptions. This seems to explain, at least in part, how Trump went from hostile to friendly toward foreign leaders like Kim Jong Un and Xi Jinping.

But if foreign leaders could figure out how to manipulate Trump’s self-righteousness, so could his domestic opposition. Harris played on that immense pride on Tuesday night.

This tactic wasn’t the only reason she won the debate (see, for example, her powerful response to the abortion question), but it was an important one.