More than anyone in the Trump administration, Mr. Kushner has cultivated Saudi Arabia’s crown prince, Mohammed bin Salman — whose family may have played a role in the disappearance of the journalist, Jamal Khashoggi — elevating the prince into a key ally in the Arab world and the White House’s primary interlocutor to the kingdom.

Mr. Kushner championed Prince Mohammed, 33, when the prince was jockeying to be his father’s heir; had dinner with him in Washington and Riyadh, the Saudi capital; promoted a $110 billion weapons sale to his military; and once even hoped that the future king would put a Saudi stamp of approval on his Israeli-Palestinian peace plan…

But if it becomes clear that the prince ordered the assassination of Mr. Khashoggi or was connected to it in some way, it will provoke an outcry on Capitol Hill; embarrass American executives, dozens of whom are flocking to Riyadh for a conference next week where the crown prince is scheduled to speak; and put Mr. Kushner, who was once himself a newspaper publisher, in an extremely awkward position.