Advisers have said Mr. Trump is poised to sign another waiver delaying the move for six more months but would balance that in a speech on Wednesday by recognizing Jerusalem as the Israeli capital. The consensus among the professionals in the room on Sunday, even those who agree on the substance, was that would be a beginner’s mistake.

Robert Wexler, the president of the S. Daniel Abraham Center for Middle East Peace and a former Democratic congressman from Florida, said Mr. Kushner and his team had earned respect for their serious efforts and for making peace a priority. “They deserve credit for that,” he said, “which makes it more bewildering why they would seemingly put all that in jeopardy by a premature announcement.”

Mr. Kushner was questioned on stage by Haim Saban, the Israeli-American entertainment mogul and prominent Democratic campaign contributor who sponsors the event. But in the course of 30 minutes, the president’s son-in-law determinedly stayed away from anything concrete.

“It’s the art of saying nothing,” said former Prime Minister Ehud Barak of Israel, who came close but failed to reach a deal with Yasir Arafat at Camp David in 2000 under the auspices of President Bill Clinton. But Mr. Barak said it would be inopportune for Mr. Kushner to get into details yet. “I don’t blame him.”

Shalom Lipner, a former adviser to seven Israeli prime ministers, including the current one, Benjamin Netanyahu, said Mr. Kushner had provided little to judge. “He came across as confident,” Mr. Lipner said. “He showed a grasp, an engagement on the issues. But the test itself will be what an actual plan looks like. That will be more telling.”

Mr. Kushner’s talk came just two days after Michael T. Flynn, the president’s former national security adviser, pleaded guilty to lying to investigators about his contacts with Russia’s ambassador during the postelection transition. Court papers indicated that he was directed to talk with the ambassador by a senior transition official who has been identified as Mr. Kushner.

Mr. Kushner was not quizzed about either development, but at one point when asked about the challenges of life at the top of the political stage, he professed not to be bothered by the slings and arrows that come with it. “We try not to be distracted by the day to day,” he said, referring to himself and his wife, Ivanka Trump. “We don’t pay a lot of attention.”