Ms. Maples said that when Mr. Trump called to console Tiffany about the death in the Maples’s family and invited his grieving daughter to visit him in New York, she urged Tiffany to go. “It gave him a chance to see her as a real person and not just a happy, smiling little girl,” she said.
Mr. Trump takes credit for his children’s sunny devotion. “I’ve always been a very good father,” he told Anderson Cooper in a Trump family interview this summer on CNN. “They come to me, friends of mine, very successful people, and their children have problems with drugs and problems with alcohol and problems with a lot of things, and they say: ‘Could you speak to my son? Could you speak to my daughter?’ And I’m always very honored to do that.”
When asked to describe his youngest daughter, Mr. Trump replied by email: “Tiffany is a tremendous young woman with a big and beautiful heart. She was always a great student and a very popular person no matter where she went. I am incredibly proud of Tiffany and how well she has done. — DJT.”
(Tiffany did not consent to be interviewed for this article, although she did pose for its photo shoot. Instead, the campaign delivered a list of approved contacts. Other family friends who were not on the list said they were instructed not to speak without authorization.)
Outside acquaintances echo that she is more serious than she looks on social media. “She didn’t seem like a party girl at all,” Carson Griffith, a writer who followed the Snap Pack around the Hamptons in 2015 for Du Jour magazine. (Ms. Griffith also occasionally writes for The New York Times.) “She stayed in the city Friday night to finish a paper, and I never saw her drink a glass of wine.” Ms. Griffith was impressed by Tiffany’s good manners: “When I would ask about her, she would say: ‘How about you? What’s your job like?’”
Tiffany’s vacations were mostly spent on trips with her mother — a mix of fun mother-daughter getaways and good-will tours overseas, like handing out vitamin C pops at an orphanage in Malawi. A bodyguard went with her on visits to her Georgia relatives, but otherwise she blended easily in her mother’s small hometown. Sometimes, her celebrity status poked through.
Recalling a party for 3-year-olds, Janice Kiker, a close family friend in Dalton, Ga., said: “Tiffany showed up in a faded, worn-out tutu. I was shocked.” She added with a laugh: “Then someone told me it had belonged to Shirley Temple. I said, ‘Never mind.’”
Lara Trump, who is married to Eric, said Mr. Trump is close to all his children. “I was struck when I first came into this family how much he is their dad,” she said by phone while campaigning for her father-in-law in Columbus, Ohio. “In public, he’s a performer. Behind closed doors, he is polite and respectful and wants to hear from other people,” Lara Trump said. She noted that Mr. Trump and Tiffany have a “fun and loving relationship” and that “he is very proud of her.”
Some observers have a less benign view of Mr. Trump’s rapport with his children. “I can say with real confidence that he spent virtually no time with them when they were young,” said Tony Schwartz, who shadowed the real estate developer for 18 months to ghostwrite Mr. Trump’s 1987 best seller, “Trump: The Art of The Deal.” Mr. Schwartz said in a recent article in The New Yorker that he now regrets the book and his role in promoting Mr. Trump.
“On the rare times Ivana brought one or two of the children to his office, he couldn’t have been less interested,” Mr. Schwartz said.
That wasn’t entirely true with Tiffany, Ms. Maples said. When Tiffany was a baby at Mar-a-Lago, he would occasionally snatch her up and carry her as he talked to electricians and carpenters building a club health spa.
Tiffany was too young to remember. “I kept pictures for her to prove it,” her mother said. (She also confirmed that Tiffany was named for one of Mr. Trump’s favorite deals: the air rights he bought above landmark store to build Trump Tower.)
Growing up, Tiffany mostly saw her father on spring break at Mar-a-Lago, though Mr. Trump visited her on occasion as well. “Whenever Tiffany got an award, he would fly to California to see her get it,” Mrs. Kiker said.
As a teenager, Tiffany seemed interested in having a show business career like her mother. She took acting lessons with her mother’s coach, and in 2011 she recorded a pop song, “Like a Bird.”
College brought Tiffany closer to her father — and her half sister. Ivanka arranged for her to have a summer internship at Vogue. After graduating last June, Tiffany spent her summer months on a paid internship in communications at Warby Parker, the eyewear company, and is studying to take the law school entrance exams.
Tiffany seems intent on staying close to her centripetal father. “Law school completely makes sense,” said Lara Maggs, a close friend from Penn. Ms. Maggs described “Tiff” as a study grind who is driven to prove herself. “A law degree would bring added value to a really accomplished family,” she said.
The Trump children aren’t the only famous scions with a rich, successful parent. Chelsea Clinton is also enmeshed in the family business.
“There are instances where demonstrating family loyalty — family love — means upholding a core identity around wealth,” said Jamie Johnson, a filmmaker and heir to the Johnson & Johnson fortune, who made “Born Rich,” a 2003 documentary about his cohorts, including Ivanka.
“The more public the family, the greater the emotional responsibility to uphold the public image,” Mr. Johnson said.
Donald Jr. and Ivanka Trump are not only consiglieri in their father’s company and his campaign, they were regulars on “The Apprentice” and stressed how hard they had to work in business to earn their father’s trust. They were privileged, but not spoiled or entitled, Ivanka said. Certainly, compared to some of their more dissipated, profligate peers in the top 0.01 percent, the Trump children are remarkably on message.
In that family interview with Anderson Cooper, Tiffany batted back a suggestion that her father was condescending and even insulting to women. “He has the utmost faith that we can accomplish whatever we set our minds to,” she said, speaking of Ivanka and herself, “just as well as men, if not more so.”
Even Mr. Trump wasn’t always sure his children would flourish under his oversize shadow. “Statistically, my children have a very bad shot,” Mr. Trump told Playboy in 1990. “Children of successful people are generally very, very troubled, not successful.”
There are not many hints of dissent or rebellion in the pack. After Mr. Trump left Ivana for Ms. Maples, Don Jr. didn’t speak to his father for a period of time. Now, if anything, Don Jr. models himself a little too closely to his father: He posts recklessly on Twitter on Mr. Trump’s behalf, most recently comparing Middle Eastern refugees to Skittles candy.
Tiffany’s friends say that she doesn’t take her father’s wealth for granted, despite some Eurotrash-y social media posts from a year ago. (One is a close-up of a bowl of caviar.)
“Unless she’s with her dad, she’s happy to fly coach,” said Lara Maggs, her friend from Penn. “When we flew together from Philly, we were in the middle seats at the back of the plane.” She said that the day before Tiffany flew to the convention, she bought the blue dress she wore for her speech at Bloomingdale’s off a sales rack.
Ivanka said she didn’t want to expose her little sister to the klieg lights of the presidential campaign before she is ready. “She will not do it if she is not comfortable with it,” she said. “Nobody is pushing her.” She added, indignantly, “People refer to us as surrogates, but we are his children.”
An earlier version of this article transposed the given and last names of a writer who has interviewed Tiffany Trump. She is Carson Griffith, not Griffith Carson.