The moment of truth for President Trump

The news broke at around 6.30pm Washington time that US bases in Iraq were under Iranian ballistic missile attack. In a city weary of debating Middle East wars there was a sense of deep alarm and foreboding.

America is facing the possibility of being dragged into a cauldron of conflict with a powerful country it has long viewed with deep suspicion and hostility.

The President huddled with his advisers in the White House. Then came his tweet that suggested that Iran’s missile salvo had not been been as destructive as feared.

• Trump: Withdrawal of troops from Iraq would be 'worst thing'

It raises the possibility that President Trump may not feel compelled to respond with a bombing raid or missile attack on Iranian targets, a further escalation that would put the two nations on an irreversible path to war.

But this remains a supremely dangerous moment. It is likely the last opportunity to pull out of the cycle of escalation.

Will the regime in Iran now feel Qassem Suleimani’s death has been sufficiently avenged? Will the White House be able to argue that deterrence has been established without a military response?

The Iranians have offered - in a striking combination of military aggression and diplomacy - an olive branch of sorts. The Foreign Minister Javad Zarif tweeted that the attack had concluded.

The next few hours will determine whether President Trump is able to show strategic restraint and whether Iran can hold back its proxies and militias across the region.

The world is watching to see whether two proud and unpredictable nations, with erratic leaders, can avoid the open warfare that would lead to cascading and catastrophic consequences across the Middle East.

The stakes could not be higher. This moment requires either Iran or the United States to step off the ladder of escalation, even at the cost of looking weak.

Will President Trump find the courage to do so? Every American President eventually faces a single, fateful decision that will define their legacy. This morning, almost exactly three years after he became Commander-in-Chief, Donald Trump faces that moment.