International diplomacy is a world of careful rituals, hierarchy and credentials. But when the Israeli ambassador to the United States, Ron Dermer, wanted to communicate with Donald J. Trump, he ended up on two occasions in the Manhattan office of a young man with no government experience, no political background and no official title in the Trump campaign: Jared Kushner.
Mr. Kushner held court at length with Mr. Dermer, doing his best to engage in the same sort of high-level conversation that the ambassador conducted with career diplomats and policy experts from Hillary Clinton’s campaign.
A 35-year-old real estate developer, investor and newspaper publisher, Mr. Kushner derives his authority in the campaign not from a traditional résumé but from a marital vow. He is Mr. Trump’s son-in-law.
Yet in a gradual but unmistakable fashion, Mr. Kushner has become involved in virtually every facet of the Trump presidential operation, so much so that many inside and out of it increasingly see him as a de facto campaign manager. Mr. Kushner, who is married to Mr. Trump’s daughter Ivanka, helped recruit a sorely needed director of communications, oversaw the creation of an online fund-raising system and has had a hand in drafting Mr. Trump’s few policy speeches. And now that Mr. Trump has secured the Republican nomination, Mr. Kushner is counseling his father-in-law on the selection of a running mate.
It is a new and unlikely role for Mr. Kushner, a conspicuously polite Harvard graduate whose prominent New Jersey family bankrolled Democrats for decades and whose father’s reputation was destroyed, in a highly public and humiliating manner, by his involvement in electoral politics.
Now, in a Shakespearean turn, Mr. Kushner is working side by side with the former federal prosecutor who put his father, Charles Kushner, in prison just over 10 years ago: Gov. Chris Christie of New Jersey, whom Mr. Trump named as a top adviser. Mr. Kushner originally voiced objections to Mr. Trump about the appointment, but Mr. Kushner and Mr. Christie have since become wary allies in seeking to impose greater discipline on Mr. Trump’s unconventional campaign.
Much about the Trump candidacy seems at odds with Mr. Kushner’s personality and biography: An Orthodox Jew and grandson of Holocaust survivors, Mr. Kushner is now at the center of a campaign that has been embraced by white nationalists and anti-Semites.
Mr. Kushner’s friends say he has expressed no concern to them about his father-in-law’s behavior. On Saturday, Mr. Trump created a firestorm after posting an image on Twitter featuring a picture of Mrs. Clinton with a six-pointed star and a pile of cash, which had previously appeared on a website known for anti-Semitism. (On Monday, Mr. Trump said on Twitter that it was not a Star of David, but a sheriff’s or a plain star.) Mr. Kushner believes that his father-in-law’s respect for his Jewish faith is sincere, his friends said, and that the issue is not worth addressing.
Mr. Kushner’s role was described in more than two dozen interviews with friends, colleagues and campaign staff members, some of whom spoke on the condition of anonymity so they could disclose interactions that were supposed to remain private. Mr. Kushner declined to be interviewed.
In many ways, he has filled a vacuum in a startlingly small organization that has had no official manager since the June ouster of Corey Lewandowski, which Mr. Kushner advocated, and that has fallen far behind in building a 50-state campaign. But his real power, his friends said, stems from his close relationship with Mr. Trump, who has long preferred the advice of family over political professionals and who sees in Mr. Kushner a younger version of himself.
“Jared is an amazing son-in-law, and we are very close,” Mr. Trump said in a statement, describing him as “a big and bold thinker.”
For both men — the privileged sons of quick-tempered and domineering real estate tycoons — the legacies of their fathers loom large. More than 30 years after Mr. Trump took command of the Trump Organization and built the Grand Hyatt Hotel and Trump Tower, Mr. Kushner tapped his own family empire, Kushner Companies, to buy a Fifth Avenue skyscraper and become part owner of a giant office complex near the Brooklyn waterfront.
“My father looked at the deals Jared was doing and saw himself in those deals,” Ms. Trump said.
But the parallels end there. Mr. Trump came to Manhattan to outstrip his father’s success; Mr. Kushner was seeking to redeem his family’s tarnished name.
The elder Mr. Kushner built the family’s real estate business into a multibillion-dollar empire of apartments and land until he was sent to federal prison in 2005 for tax evasion, witness tampering and illegal campaign donations, many of them to Democratic candidates.
The case involved a traumatic and tawdry family feud: At one point, Charles Kushner sought to retaliate against his brother-in-law, who was cooperating with the federal authorities, by hiring a woman to seduce him and videotape the encounter. “Vile and heinous” was how Mr. Christie, then the United States attorney for New Jersey, described the conduct.
Almost overnight, Mr. Kushner, 24 years old and still a student at law school, became the public face of the family business. On weekdays, he toured construction sites; on weekends, he flew to Alabama to visit his father in prison. The two remain exceedingly close: For years, Mr. Kushner used a wallet that his father had made in prison.
Mr. Kushner does not like to talk about his father’s travails, but they plainly left a mark on him. At his son’s recent bris, he spoke of his wish for the newborn: “May life be hard enough that you grow, but not so hard that you break.”
In 2006, with the family’s wounds from the scandal still fresh, Mr. Kushner bought The New York Observer, a small newspaper aimed at the city’s social, political and real estate elite. A stranger to the culture of a publication that delighted in needling the rich and powerful, he initially floundered as a publisher, alienating reporters and cycling through a series of editors before landing on an old friend of the Kushner family, Ken Kurson. In April, the newspaper, which under its previous ownership made a sport of mocking Mr. Trump, enthusiastically endorsed his presidential bid.