An unwritten pact binding the U.S. and Saudi Arabia has survived 15 presidents and seven kings through an Arab oil embargo, two Persian Gulf wars and the Sept. 11 terrorist attacks. Now, it is fracturing under two leaders who don’t like or trust each other. Saudi Crown Prince Mohammed bin Salman, the kingdom’s 37-year-old day-to-day ruler, mocks Biden in private, making fun of the 79-year-old’s gaffes and questioning his mental acuity... He has told advisers he hasn’t been impressed with Mr. Biden since his days as vice president, and much preferred former President Donald Trump ... Mr. Biden said on...