Saudi Arabia even announced that Crown Prince Mohammed bin Salman, who almost everybody believes must have approved this operation — his initials, M.B.S., are now said to stand for “Mr. Bone Saw” — will lead an investigation into what happened. That’s like appointing O.J. Simpson to investigate the murder of Nicole Brown Simpson.

These lies are so blatant and implausible that they underscore how out of touch M.B.S. is, and also suggest M.B.S. believes that he will have the backing of the United States in this cover-up. That’s a good bet, since Trump has lately celebrated the assault on a journalist by a Montana congressman and previously suggested that maybe a rogue killer was responsible for killing Jamal.

But M.B.S. has already gotten away with kidnapping Lebanon’s prime minister and starving eight million Yemenis; if he also gets away with murdering Jamal, who was an American resident and Washington Post columnist, as many believe happened, then that’s a green light to him and any other autocrat who wants to make a troublesome journalist disappear. Journalists and democracy activists all over the world will have targets on their backs.

So what we really have now is a test of Trump and of America itself. Will Trump go along with the cover-up, or will he attempt to uphold America’s honor and dignity in this instance? Here’s what he should do:

1. Since this happened in a NATO country, the NATO nations should jointly seek a United Nations-backed international investigation of the murder. This could be ordered by the United Nations Security Council, the General Assembly or the Human Rights Council.

2. The NATO countries should, in coordination, expel all Saudi ambassadors.

3. NATO countries should suspend all weapons sales, including of spare parts for aircraft, to Saudi Arabia. This would put substantial pressure on Saudi Arabia, which depends on the United States for its security.