Hillary Clinton knew exactly what she was doing at the first presidential debate when she mentioned Alicia Machado, the Venezuelan Miss Universe who provoked Donald Trump’s ire in the 1990s by gaining weight.

She wasn’t just depicting Trump as a creep who “hangs around beauty pageants” and who insults women (he called Machado “Miss Piggy”) and Hispanic immigrants (he also called her “Miss Housekeeper”). She wasn’t just using Machado, who became an American citizen this year, to urge people to register to vote. She was hoping to draw her opponent into one of his signature self-inflicted damaging news cycles.

And it worked. Trump has been relentlessly, publicly attacking Machado all week, most recently in a string of tweets at 5 am. His reaction proves he’s easy to bait, and demonstrates how badly Trump’s life experiences — his business career and his reality TV show — have prepared him for the presidency.

Trump is seemingly incapable of letting any attack on his character go unanswered, no matter how much he might damage his own prospects in the process. It’s why he spent days attacking first a Mexican-American judge and then the Muslim father of a fallen soldier. His habit of starting feuds might have served him well in the real estate business, where his status as a tabloid celebrity helped him get attention, and on reality TV, where viewers tune in for the unfolding drama.

It’s one thing to fight with your ex-wife in the tabloids in 1980s New York or provoke contestants to spar with each other on The Apprentice. It’s quite another to start a tabloid-style feud against a federal judge, the father of a war hero, or a beauty queen. But Trump seemingly can’t stop himself from picking these fights, no matter how damaging they might be.

Alicia Machado is a Venezuelan beauty queen and part of an elaborate trap Hillary Clinton set

Clinton brought up Alicia Machado at the first presidential debate as an example of how Donald Trump treats women, valuing them on their looks above all else and not hesitating to insult them when they fall short of his standards. Clinton — already aware that Trump was struggling with Latino voters and women of all races — sprang at the opening when moderator Lester Holt brought up Trump’s attacks on her.

“He called this woman Miss Piggy. Then he called her Miss Housekeeping, because she was Latina,” Clinton said at the debate Monday night. “Donald, she has a name. Her name is Alicia Machado.”

But Machado was, in other ways, a bigger symbol for the campaign. Originally from Venezuela, she became a citizen to register to vote against Trump — and the Clinton campaign needs Latinos, as well as other Trump opponents, to do the same this fall. She’s a reminder of Trump’s attitude toward women, another group whose enthusiastic support Clinton needs to win.

And Clinton clearly hoped to lure Trump into a fight with Machado that would touch on another campaign theme: He’s easily provoked and can’t be trusted with power.

Machado had been telling her story, without much notice, in the media for months. She won Miss Venezuela in 1995 and Miss Universe in 1996, the year Trump bought the pageant. In the year she wore the crown, she gained about 40 pounds and asked the Miss Universe organization to help her lose it, she told the New York Times in May.

Trump was outraged. He called Machado an “eating machine” on The Howard Stern Show. He invited reporters to watch her exercise at a gym and told them, “This is somebody who likes to eat,” claiming she’d gained “60 or 70 pounds.” He even disparaged Machado in his 1997 book, The Art of the Comeback:

I could just see Alicia Machado, the current Miss Universe, sitting there plumply. God, what problems I had with this woman. First, she wins. Second, she gains fifty pounds. Third, I urge the committee not to fire her. Fourth, I go to the gym with her, in a show of support. Final act: She trashes me in the Washington Post

Clinton had clearly selected Machado as a symbol well in advance, making her the subject of bilingual anti-Trump ads. The morning after the debate, Machado was profiled in the New York Times, interviewed by the Guardian, and featured in Cosmopolitan magazine, all articles that required some preparation.

Featuring Machado was, in some ways, a gamble on the campaign’s part; she’s lived what could be described as an eventful life. After her tenure as Miss Universe, she was accused of being an accomplice to a murder attempt by her then-boyfriend (charges were later dropped) and threatening a judge. She became a telenovela actress and participated in a Spanish reality TV show but was kicked off for having sex with another contestant (which was captured on camera, albeit vaguely).

“Everybody has a past,” Machado said this week. “And I’m not a saint girl.”

It turns out, though, that what otherwise might be liabilities in Machado’s background also made her perfect bait for Trump, who can’t be attacked without attacking in turn.

Donald Trump can’t take criticism without starting a feud

The usual way to dispel an effective attack in a political campaign is for the candidate to acknowledge it as little as possible and immediately change the subject to something more flattering, or to claim that the American people don’t really care about this at all.

Then there is the Trump way, which is to keep talking about the original story and how wrong and bad it is for as long as possible — ensuring that the negative story sticks around, generating new, damaging headlines, day after day.

So Trump spent most of the week after the first debate talking about Machado, Clinton, and how unfair Clinton’s attack was. Every time Trump attacked Machado, it led to another round of coverage, and let everyone whose attention might have wandered at the very end of the debate know that Trump once mocked a Latina beauty queen for her weight and her ethnicity.

On Fox & Friends the morning after the debate, Trump continued to defend his actions in the 1990s: “She was the winner and, you know, she gained a massive amount of weight, and it was a real problem.” Then, early Friday morning, he issued a string of vitriolic tweets about Machado, accusing Clinton of helping her gain citizenship, alluding to the more controversial parts of her past, and urging everyone to “check out [her] sex tape.”

There is no evidence Clinton helped Machado gain citizenship. The “sex tape” Trump referred to is grainy footage of two people under blankets on a Spanish reality TV show; as Snopes pointed out, it’s barely explicit and, given the provenance, possibly manipulated.

“This, of course, is not the first time the candidate insists on discrediting someone or insists on demoralizing women, minorities, and people of certain religions through his hateful campaign,” Machado said in a statement on Instagram. “This is definitely one of his most frightful characteristics. Through his attacks, he's attempting to distract from his campaign's real problems and his inability to be the leader of this great country.”

The Clinton campaign, on Clinton’s Twitter account, argued that Trump’s response should be disqualifying:

When something gets under Donald's thin skin, he lashes out and can't let go. This is dangerous for a president. — Hillary Clinton (@HillaryClinton) September 30, 2016

Trump, meanwhile, said that his early morning tweeting proved what a vigilant president he would be:

For those few people knocking me for tweeting at three o'clock in the morning, at least you know I will be there, awake, to answer the call! — Donald J. Trump (@realDonaldTrump) September 30, 2016

But irrational attacks on ordinary people who attacked him are becoming a pattern for Trump. When Judge Gonzalo Curiel, who is overseeing a lawsuit against Trump University, handed down a decision Trump didn’t like, Trump said that his Hispanic heritage meant that he was unable to judge the case fairly. Speaker of the House Paul Ryan called it “the textbook definition of a racist comment.” Trump continued to repeat the attack in interviews, drawing more attention not just to his comments but to the lawsuit against one of his businesses.

When Khizr Khan, the father of an American soldier who died in Afghanistan, criticized Trump’s position on Muslims at the Democratic National Convention, Trump speculated the next day that he wasn’t allowing his wife to speak. Then while Khan gave an interview on CNN, he tweeted that he had been “viciously attacked” from the stage.

The Khan controversy lasted for nearly a week and drew a rebuke from John McCain. It polled very badly. And it means that Khan — whose speech was powerful but wasn’t aired during primetime — got much more airtime than he otherwise would had.

Trump sometimes starts a fight even when he’s not the one who was attacked in the first place, as in Ivanka Trump’s recent interview with Cosmopolitan. It was a tough interview for his daughter, who struggled in places to keep her cool — even ending the interview abruptly. But when Trump started criticizing the magazine and reporter Prachi Gupta, it ensured the interview would get much more attention than it already had.

Trump’s feuds make sense for a reality TV star. They’re scary for a president.

Trump could have learned from the Khan controversy and issued a statement saying that what seemed appropriate as a beauty pageant owner in 1996 looks, with the benefit of hindsight, embarrassing for a would-be president in 2016, and apologized. Or he could have changed the subject and said he’s focused on what voters really care about: the economy, not B-list celebrity gossip from 20 years ago.

But if Trump did that, he wouldn’t be Trump. He never backs down or admits error or apologizes. Instead, he starts feuds. It’s not a political strategy; it’s a personal vendetta.

For years, this made sense as a strategy for Trump, who spent decades in the macho world of New York real estate and has long held the mantra that any publicity is good publicity. Feuds get you in the headlines of tabloids. They drive the drama on reality TV. In exchange, the celebrities or contestants involved get what they crave: attention. Until Trump started running for president, his livelihood depending on generating that kind of attention to make him stand out from the pack.

When two celebrities are leaking details of their fights to the tabloids, or two reality TV contestants are sparring, we’re all in on the joke. We all know the drama is exaggerated, and that at the end of the day, everyone will go home with more money and more power than they had before.

But the vendettas look different when one person is the potential next leader of the free world and the other is a private citizen. If Trump uses his campaign to heckle and criticize ordinary people — a Muslim father, a Venezuelan beauty queen, a Mexican-American judge — it’s reasonable to wonder about how he would treat the people who anger him when he has more power than just an early morning tweetstorm at his disposal.

Even many of Trump’s supporters, about one-third, say in polls that they’re concerned about his temperament and judgment. This is why Machado was a particularly important find for the Clinton campaign. She doesn’t just embody the worst of what Trump has done in the past, but his reaction to her suggests what he might do in the future.

Watch: This election is about normal vs. abnormal