U.S. President Donald Trump, speaks with Mohammed bin Salman, the Kingdom of Saudi Arabia's deputy crown prince and minister of defense, left, in the Oval Office of the White House in Washington, D.C., U.S., on Tuesday, March 14, 2017.

DUBAI – Even in a region that specializes in nightmare scenarios, the "war game" below got my attention because it falls within the realm of the possible and the horrible.

What makes it even more explosive is the context. The toxic aftermath of Saudi journalist Jamal Khashoggi's murder has allies feuding, adversaries scheming, and competitors jockeying for influence among Muslims worldwide.

One possible outcome in the below scenario is the worst regional war the Middle East has seen. Another could be a historic rupture in U.S. relations with Saudi Arabia.

A Middle Eastern government analyst, when asked what risk keeps him awake at night, frames the scenario this way:

Iranian-backed Houthi militia in Yemen break a fragile cease-fire with a missile launched at Riyadh, the Saudi capital. Unlike so many before it, this missile slips through Saudi air defenses and lands on a shopping mall in early evening, the busiest time of the day. The strike takes mass casualties and sets off panic. Saudi Crown Prince Mohammed bin Salman, already rattled by U.S. and European backlash from the Khashoggi killing, blames Tehran for the attack, knows he must respond, but is unsure what allies he can count on. Advisors argue he must strike Iran itself, given the scale of the carnage, the pointlessness of striking targets in Yemen, and questions swirling about his leadership. However, he lacks the offensive and defensive wherewithal for a sustained war with Iran. He considers two options: a secure call to President Donald Trump to request he join his Saudi allies against their common foe. Or, alternatively, the Saudi Air Force strikes Iran, provoking a counterstrike that it hopes will bring American allies into the fighting. In either case, the U.S. president is left to decide: double-down on a tainted ally or stand aside and risk those consequences.

This is just one of many perilous scenarios that experts in the region are discussing as potential "aftershocks" from the Khashoggi killing.

What U.S. allies worry about most are the consequences of understandable U.S. and European reaction to the murder –brutal, foolish and irresponsible as it was – that disregards the risk of weakening U.S. alliances, strengthening the already growing role of China and Russia, and fueling pan-Islamist momentum.

Most of all, they worry about a slowing or even a reversal of moves over the last two years by the Saudi crown prince to turn his kingdom against the support and financing of Islamist extremism that was in no small part a result of previous Saudi leadership.

The ongoing Saudi affair highlights a historic tension in U.S. foreign policy between American values and interests. Without its values as a guide, the United States loses its unique attraction as a global power. Yet values alone would have failed to win the Cold War against the Soviet Union – and will likely fail now in the Middle East as well.

The Wall Street Journal editorial board this week joined a chorus of criticism of Trump's statement this week that leaned toward all interests and no values. "Ronald Reagan," said the Wall Street Journal, "pursued a hard-line, often controversial foreign policy against Soviet Communism, but he did so with a balance of unblinkered realism and American idealism. Mr. Trump seems incapable of such balance."