Some Democrats are calling on the president to revoke Mr. Kushner’s security clearances. Representative Adam B. Schiff, Democrat of California and a chairman of the House committee investigating Russian efforts to sway the 2016 election, suggested in an interview on Sunday that the recent news reports about Mr. Kushner have brought the investigation from the periphery of the Trump campaign and transition teams into the Oval Office.
“If these stories are accurate” in their description of Mr. Kushner and Michael T. Flynn, Mr. Trump’s ousted national security adviser, “were they acting at the behest of Mr. Trump, then-candidate, or President-elect Trump? But whether they were or not, they’re still significant.”
In a statement Sunday night, Mr. Trump praised his son-in-law and the work he has done in the White House.
“Jared is doing a great job for the country,” he said. “I have total confidence in him. He is respected by virtually everyone and is working on programs that will save our country billions of dollars. In addition to that, and perhaps more importantly, he is a very good person.”
But in recent weeks, the Trump-Kushner relationship, the most stable partnership in an often unstable West Wing, is showing unmistakable signs of strain.
That relationship had already begun to fray a bit after Mr. Trump’s dismissal of the F.B.I. director, James B. Comey, which Mr. Kushner had strongly advocated, and because of his repeated attempts to oust Stephen K. Bannon, Mr. Trump’s chief strategist, as well as the president’s overburdened communications team, especially Sean Spicer, the press secretary.
It has been duly noted in the White House that Mr. Trump, who feels that he has been ill served by his staff, has increasingly included Mr. Kushner when he dresses down aides and officials, a rarity earlier in his administration and during the campaign.
The most serious point of contention between the president and his son-in-law, two people familiar with the interactions said, was a video clip this month of Mr. Kushner’s sister Nicole Meyer pitching potential investors in Beijing on a Kushner Companies condominium project in Jersey City. At one point, Ms. Meyer — who remains close to Mr. Kushner — dangled the availability of EB-5 visas to the United States as an enticement for Chinese financiers willing to spend $500,000 or more.
For Mr. Trump, Ms. Meyer’s performance violated two major rules: Politically, it undercut his immigration crackdown, and in a personal sense, it smacked of profiteering off Mr. Trump — one of the sins that warrants expulsion from his orbit.
In the following days during routine West Wing meetings, the president made several snarky, disparaging comments about Mr. Kushner’s family and the visas that were clearly intended to express his annoyance, two aides said. Mr. Kushner did not respond, at least not in earshot.
His preppy aesthetic, sotto voce style and preference for backstage maneuvering seemingly set him apart from his father-in-law — but the similarities outweigh the differences. Both men were reared in the freewheeling, ruthless world of real estate, and both possess an unshakable self-assurance that is both their greatest attribute and their direst vulnerability.
Mr. Kushner’s reported feeler to the Russians even as President Barack Obama remained in charge of American foreign policy was a trademark move by someone with a deep confidence in his abilities that critics say borders on conceit, people close to him said. And it echoes his history of sailing forth into unknown territory, including buying a newspaper at age 25 and developing a data-analytics program that he has said helped deliver the presidency to his father-in-law.
He is intensely proud of his accomplishments in the private sector and has repeatedly suggested his tenure in Washington will hurt, not help, his brand and bottom line.
That unfailing self-regard has not endeared him to the rest of the staff. Resentful Trump staff members have long talked about “Jared Island” to describe the special status occupied by Mr. Kushner, who, in their view, is given license to exercise power and take on a vague portfolio — “Middle East peace” and “innovation” are its central components — without suffering the consequences of failure visited by the president on mere hirelings.
Adding to the animus is Mr. Kushner’s aloof demeanor and his propensity for avoiding messy aspects of his job that he would simply rather not do — he has told associates he wants nothing to do with the legislative process, for instance. He also has a habit, they say, of disappearing during crises, such as his absence on a family ski trip when Mr. Trump’s first health care bill was crashing in March.
Mr. Bannon, a onetime Kushner ally turned adversary known for working himself into ill health, has taken to comparing the former real estate executive to “the air,” because he blows in and out of meetings leaving little trace, according to one senior Trump aide. Just as Mr. Trump does, Mr. Kushner quickly forms fixed opinions about people, sometimes based on scant evidence. But Mr. Kushner is quicker to admit when he has misjudged a situation, and to change course.
Despite the perception that he is the one untouchable adviser in the president’s inner circle, Mr. Kushner was not especially close to his father-in-law before the 2016 campaign. The two bonded when Mr. Kushner helped to take over the campaign’s faltering digital operation and to sell a reluctant Rupert Murdoch, the chairman of Fox News’s parent company, on the viability of his father-in-law’s candidacy by showing him videos of Mr. Trump’s rally during a lunch at Fox headquarters in mid-2015.
When asked by friends and associates to describe the source of his influence over the president, Mr. Kushner has offered explanations rooted in loyalty, family and, above all, his acceptance that Mr. Trump is a 70-year-old man of fixed habits who cannot be easily diverted from a course of action.
Mr. Kushner is fond of telling friends that he does not have “any vested interests” beyond seeing his father-in-law succeed. Many of the people working for Mr. Trump are not “looking out for the boss, but I am,” Mr. Kushner told a visitor recently.
“My job is to put him in a good place,” Mr. Kushner told another person he spoke to before embarking on the Middle East leg of Mr. Trump’s trip, which he planned.
Often, that entails soothing Mr. Trump. Other times, he serves as a goad, as he did in urging Mr. Comey’s ouster and assuring Mr. Trump that it would be a political “win” that would neutralize protesting Democrats because they had called for Mr. Comey’s ouster over his handling of Hillary Clinton’s use of a private email server, according to six West Wing aides.
Mr. Kushner’s war with Mr. Bannon has been a damaging distraction. Several upper-level staff members said Mr. Kushner has made it plain to them that they needed to choose sides or be iced out from an increasingly influential team that includes Gary D. Cohn, the director of the National Economic Council, and a handful of other Kushner-allied power brokers like Dina Powell, a national security official.
Mr. Kushner remains infuriated by what he believes to be leaks about his team by Mr. Bannon, who has privately cautioned Mr. Trump against being “captured” by liberal, New York “globalists” associated with his son-in-law, according to three people close to the president.
Mr. Trump, however, has had enough. He recently chided Mr. Kushner for continuing to call for Mr. Bannon’s ouster, saying he would not fire his conservative populist adviser — who has deep connections with Mr. Trump’s white, working-class base — simply because Mr. Kushner wanted him out, according an administration official.
Mr. Trump admires Mr. Kushner’s tough streak, and shares his taste for payback, especially in defense of his family. Over the years, former employees said, Mr. Kushner has quietly sought revenge on enemies whom he sees as hostile to another scandal-buffeted man in his life — his father, Charles Kushner, a New Jersey-based real estate tycoon who was imprisoned for, among other crimes, efforts to retaliate against his sister for cooperating with a federal inquiry targeting him.
As owner of The Observer, a once-edgy, salmon-hued broadsheet he purchased when he was 25, Mr. Kushner pushed for negative articles his editors viewed as vehicles for personal animus. The Observer’s targets included The Star-Ledger in Newark, whose coverage of Charles Kushner’s case angered the family; a little-known banker who apparently had irked the elder Mr. Kushner; and a lender who had refused Jared Kushner’s request to forgive part of the family’s debt on a Fifth Avenue skyscraper.
Ken Kurson, a friend of Mr. Kushner’s who until this month was the editor in chief of The Observer, said accusations about personal score-settling were “complete nonsense,” adding that story ideas “can and should come from anywhere.”
Mr. Kushner sees his role as a freelance troubleshooter, but he has focused on foreign policy, friends say, because he saw a gap in the White House structure in that area.
Top administration officials know the importance of cultivating him: Last month, he traveled to Iraq at the invitation of Gen. Joseph F. Dunford Jr., the chairman of the Joint Chiefs of Staff, and he serves as a sounding board for officials like Lt. Gen. H. R. McMaster, the national security adviser, according to Elliott Abrams, a Republican foreign policy veteran whom Mr. Trump vetoed for a job in the State Department.
“I hear more worries about the president than about Jared,” he said. “In fact, I never hear complaints about Jared.”
Jason D. Greenblatt, the White House adviser on international negotiations, said that on the Middle East, at least, Mr. Kushner is not just a sounding board, but an adviser who helps shape policy options for the president. Together with Secretary of State Rex W. Tillerson and others, he said, Mr. Kushner helps shape policy decisions to put before the president. He said Mr. Kushner deserves a substantial part of the credit for Mr. Trump’s recent trip to the Middle East. “Jared put together all the moving parts,” he said. “It went great.”
With a staff of about a half-dozen, Mr. Kushner has also created an office for innovation that is tackling a disparate array of projects, from promoting apprenticeship programs as an alternative to four-year college degrees to modernizing how the government buys software.
Eric Schmidt, the executive chairman of Alphabet, Google’s parent company, said in an email, “His passion on this is very real.”
So far, on some issues, the innovation office’s role seems mostly advisory. David Shulkin, the veterans affairs secretary, said he meets with Mr. Kushner about twice a month to discuss his plans to modernize the agency.
Asked for a concrete example of how Mr. Kushner’s office has helped him, Mr. Shulkin said aides were pulling together corporate leaders who hired a lot of veterans, “and that’s important.”
But the Russia investigation has shaken Mr. Kushner, friends and associates say. When news broke last week, Mr. Kushner and his wife at first discussed getting a statement denying the report issued through the White House counsel, Donald F. McGahn II — who told them that it was not a good precedent to set and that it was a job for a personal attorney.
While Mr. Kushner has said he and his wife might move back to Manhattan if it were best for their family, he appears, for now, willing to stay and fight.
Senator Bob Corker of Tennessee, the chairman of the Foreign Relations Committee, said in an appearance on NBC’s “Meet the Press” on Sunday that White House officials had reached out to reassure him that Mr. Kushner was willing to cooperate in the inquiry into possible collusion between the Russians and Trump aides. “He seems to be a very open person,” Mr. Corker said of Mr. Kushner. “I’d let him speak for himself when the time is right.”