Donald Trump marks the opening of his Trump Taj Mahal Casino Resort in Atlantic City on April 5, 1990. (Mike Derer/AP)

The attacks began to fly soon after Tarla Makaeff filed a 2010 fraud lawsuit against Trump University.

First, Donald Trump filed a potentially ruinous defamation suit against the onetime customer of his real-estate seminar business. That case was tossed out by a judge, but it launched a recurring counteroffensive by Trump that put Makaeff “through the wringer,” according to her lawyers in a court filing, and has coincided with his presidential candidacy.

Trump blasted the California yoga instructor during a presidential campaign rally, calling her a “horrible, horrible witness,” and then tweeted that she was “Disgraceful!”

This spring, Makaeff persuaded the judge presiding over the Trump University case to let her remove her name as a plaintiff. She did not respond to a recent request for comment, choosing to step back into obscurity, out of the line of fire.

Tarla Makaeff at her home in Irvine, Calif., in 2008. Makaeff was a plaintiff in a lawsuit against Republican presidential candidate Donald Trump's Trump University. (Nick Koon/Orange County Register via AP)

Over decades in business, through his well-publicized romantic entanglements, and now as a presidential candidate, Trump has demonstrated that those who rise up to criticize him do so at their own peril.

He deploys an array of tactics to fight back — countersuits, threats and personal insults, among others — while using stringent confidentiality agreements to guard against insider accounts from employees, business partners, his former spouses and now his campaign staffers.

Trump’s tactics were apparent this week when court filings revealed that he has sought $10 million in damages from Samuel Nunberg, alleging that the former campaign consultant violated a nondisclosure agreement by leaking confidential information to the press, according to a document provided by Nunberg’s lawyer.

“Anybody who attacks him, it’s like buyer beware,” said Louise Sunshine, who has known Trump since the 1970s and worked closely with him as he set about reshaping Manhattan’s skyline.

“Donald is very thin-skinned,” she said. “He takes everything personally. Everything.”

The approach may have worked well for a real-estate mogul who built a brand around his image as a hard-driving entrepreneur with a playboy lifestyle. But it underscores a fundamental question about Trump’s candidacy: How would a chief executive, who has never held political office and is accustomed to commanding his own empire, function as a democratic leader, as which he must interact regularly with adversaries and critics?

With the GOP convention nearing, Trump has signaled that he may try to make peace with some former rivals, offering Sen. Ted Cruz (R-Tex.) a speaking slot, for instance. But the tension between his past treatment of critics and the traditional nature of political engagement has also gained attention.

Trump has continued to needle his detractors, even those whose support he needs, as he did on a recent visit to Capitol Hill, where he attacked some Republican lawmakers. “You’ve been very critical of me,” he told Sen. Jeff Flake (R-Ariz.), according to officials with knowledge of the closed-door meeting.

He has banned various news organizations, including The Washington Post, from obtaining credentials to cover his events, citing his anger at articles or headlines.

If he wins the presidency, Trump has indicated he would try to curb critics, vowing to “open up” libel laws, and suggesting he would require senior federal employees to sign nondisclosure agreements to prevent kiss-and-tell accounts of what goes on inside a Trump White House.

“When people are chosen by a man to go into government at high levels and then they leave government and they write a book about a man and say a lot of things that were really guarded and personal, I don’t like that,” Trump told The Post earlier this year.

Legal experts suggest such a tactic could violate federal protections like the Freedom of Information Act. But Trump has seen what can happen when former employees pick up their pens.

In 1991, John O’Donnell, who worked for Trump for three years, becoming president of Trump Plaza Hotel and Casino in Atlantic City, published “Trumped! The Inside Story of the Real Donald Trump.” In it, O’Donnell departed from the self-congratulatory narrative Trump has created in a series of autobiographies and instead portrayed the developer as a crude bully who knew little about the casino business.

O’Donnell, who said in an interview that he did not sign a nondisclosure agreement with Trump, recalled that before the book was published, Trump sent an attorney to his office who threatened to link O’Donnell with illegal business activities and an extramarital affair.

“He did try to intimidate me,” said O’Donnell, who wrote about the attorney’s visit in the book. “Thank goodness, both of those things weren’t true.”

Trump denied the accusations through a spokeswoman, dismissing O’Donnell as “a disgruntled former employee.”

Trump prevented his first wife, Ivana, who collaborated with him on numerous major building projects, from writing about their partnership. She signed an agreement barring her from publishing a “diary, memoir, letter, story, photograph, interview, article, essay, account, or description or depiction of any kind whatsoever, whether fictionalized or not, concerning her marriage to [the husband] or any other aspect of [the husband’s] personal, business or financial affairs” without Trump’s consent.

The restrictive language surfaced in a 1992 New York State Supreme Court case, Trump v. Trump, in which the couple tussled over the terms of their postnuptial agreement.

In 2000, it looked as if Trump’s second wife might spill some beans after the celebrity press ReganBooks announced plans to publish a “candid memoir” by Marla Maples.

“All that Glitters is Not Gold” was to be a “cautionary tale,” said Susan Crawford, then Maples’s literary agent.

But Crawford, who recalled taking the service elevator up to the private Trump Tower suite to work with Maples on the book, said in an interview that the project never came to pass.

Quite suddenly, after Trump and Maples divorced, Crawford said, “Marla called and said, ‘Susan, I can’t do it.’ ”

Crawford said she still doesn’t know what inspired Maples’s change of heart. At the time, Trump seemed to suggest he had silenced his former wife: “She signed a confidentiality agreement,” he told the New York Times. Neither Maples nor Trump responded to requests for clarification.

Donald Trump's then-campaign manager Corey Lewandowski walks a rope line as the candidate signs autographs during a campaign stop at the First Niagara Center in Buffalo. (John Minchillo/AP)

Donald Trump and Marla Maples at Trump Plaza in Atlantic City in 1991. (AP)

Some campaign staffers have described how Trump, as a presidential candidate, zipped their lips through unusually restrictive nondisclosure agreements.

Former Trump campaign manager Corey Lewandowski has been hired as an analyst for CNN, but it is not clear whether he can comment freely about his former boss. Lewandowski earlier quashed rumors he was planning to write a book by tweeting that “I am under a strict confidentiality agreement with Mr. Trump.”

One such document, obtained by The Post, includes a “no-disparagement” clause that requires staffers to promise “during the term of your service and at all time thereafter” not to “demean or disparage publicly” Trump, his business ventures or any of his family members or their business ventures “and to prevent your employees from doing so.”

While it is not unusual for campaigns to sign NDAs with vendors and set ground rules for staff interactions with reporters, not all campaigns require staffers to sign NDAs, according to John Weaver, a Republican strategist.

“It’s not normal language for a campaign, but it doesn’t sound abnormal for Trump World,” said Weaver, who said busi­ness­ executives often fail to understand that there are “no secrets in politics.”

Trump’s current legal battle with Nunberg, the former campaign consultant, for allegedly violating his NDA, became public after Nunberg filed a petition on Tuesday in New York’s State Supreme Court to stop Trump’s $10 million arbitration claim. The petition accuses the Trump campaign of “attempting to bully Mr. Nunberg into silence, although he has not disparaged Mr. Trump or any other entity referred to in the Agreement.”

Trump’s attorney, Alan Garten, said Nunberg was “looking for free publicity using categorically false claims.” He said Nunberg was bound by a confidentiality agreement that is “standard practice for all major businesses, organizations and other entities dealing with proprietary information.”

“When the agreements are not adhered to, [Trump] will enforce them to the full extent of the law, and Mr. Trump’s litigation track record on such matters is outstanding,” Garten said.

Trump campaign spokeswoman Hope Hicks said all staffers sign NDAs, though she did not discuss their terms. The campaign of presumptive Democratic nominee Hillary Clinton did not reply to numerous emails asking about its contractual arrangements with staffers.

Many confidentiality agreements never get tested in court because they scare employees who signed them into silence, legal experts say. “The ‘in terrorem’ effect is the most valuable part,” said Cynthia Estlund, a professor of labor law at New York University School of Law.

Even people whose interactions with Trump have been largely positive are wary of saying anything that could be construed as critical.

“I don’t want to get on the wrong side of Trump,” said one former campaign staffer, who said he left on good terms but was intimidated by the legal language. “I couldn’t afford to defend myself.”

Sam Solovey, a contestant on Trump’s reality TV show, “The Apprentice,” who went on to work alongside Trump, said his boss was “always kind and generous and charming.” But, said Solovey, “I don’t want to drum up conflict because I know his penchant: He’ll be critical back even harder and stronger. I can’t fight that. I’d rather be a neutral player.”

And Trump, said Sunshine, who remains friendly with her former boss, doesn’t forgive or forget. “If you let him down, betray him, you only have one shot at it,” she said. “There’s no going back.”

Marvin Roffman learned that in 1990 after he expressed doubts about Trump’s new Atlantic City project, the Trump Taj Mahal. Roffman, a securities analyst for the Philadelphia-based investment company Janney Montgomery Scott, recalled numerous telephone calls with Trump.

He was always “charming and wonderful as long as you say what he wants to hear,” Roffman said in a recent interview. But “if you are critical or say something that is contrary to his thinking, forget it,” said Roffman. “He turns like a light switch.”

Roffman, who had covered casino gambling since the boom of the late ’70s, drew Trump’s ire after he told the Wall Street Journal that despite the excitement surrounding the opening of the Taj, he didn’t think Trump’s latest casino would last long: “Once the cold winds blow from October to February, it won’t make it,” Roffman predicted. “The market just isn’t there.”

Trump wrote to the investment company’s chief executive, threatening “a major lawsuit,” according to a copy of the letter reviewed by The Post. That letter, on Trump Organization letterhead, demanded that Roffman make “a major public apology” or that Janney fire him. Roffman signed a letter of apology that he said was drafted by the firm.

But the next day, according to Roffman, Trump made further demands. At that point, Roffman sent a second letter, against the advice of his bosses, retracting his apology. In response, Trump wrote to Roffman: “Only a fool, a highly unstable one at that, would send [such] a letter. . . . I look forward to seeing you and your firm in court.”

Trump did not respond to a request for comment. A spokeswoman for Janney also declined to comment, saying that nobody involved remains at the firm today.

Roffman lost his job but was ultimately proved right: In 1991, the Taj corporation filed for bankruptcy.

The securities analyst decided to fight back. He sued Trump in U.S. District Court in Pennsylvania for defamation of character and for damaging his business relationships.

Roffman, who estimates that his legal costs were “in the seven figures,” described the emotional impact as “horrendous. . . . It really affects your mental health,” he said. Roffman won’t reveal the terms of the settlement he eventually reached with Trump because he is bound by a confidentiality agreement that he doesn’t want to risk breaching.

Like Makaeff, the former Trump University customer, Roffman doesn’t want to tangle with Trump anymore.

“I’m 76, and I don’t feel like going through that again,” he said.