The Kingdom of Saudi Arabia has hurt itself badly with the killing of journalist Jamal Khashoggi, and its serial explanations are compounding the damage. President Trump will lose control of the Saudi-U.S. relationship if he doesn’t speak truth to these Saudi abuses and to Crown Prince Mohammed bin Salman, the 33-year-old power in front of the throne.

The most complete Saudi statement, issued late Friday night, at least admits that Khashoggi was killed in its Istanbul consulate at the hands of Saudi agents. But the story that...