As early as tonight, President Joe Biden will authorise US military action in the Middle East.
It is likely to be one of the most consequential decisions of his presidency.
At stake, the credibility of American deterrence and the teetering stability of the region.
The American president will hope his choice in the coming hours will deter any such escalation. It may do the opposite.
America’s enemies have crossed a line: Inaction is not an option, but over-reacting could light the tinderbox of Middle East tensions and ignite a regional war.
For weeks, Iranian-backed militia have been launching attacks on US assets without inflicting casualties.
That changed when a drone penetrated defences at a desert base in Jordan and reached a tent full of sleeping American soldiers.
Three are dead and more than 40 injured in the attack – blamed on a militia group with close ties to Iran.
In the hours since, President Biden will have been given a range of options by his military advisers ranging from the symbolic to the severely punitive.
He could attack the group responsible, but that will seen by many back home as weak and not striking the heart of the problem: the group’s patrons in Iran.
Also on the Pentagon’s list of options, action against the Iranian Revolutionary Guards Corps in the region outside Iran or, attacking Iranian assets within its borders.
Biden will not just be weighing geopolitical factors but domestic political considerations too.
His Republican rivals are baying for attacks on Iran itself. He cannot afford to look weak in an election year.
But another costly foreign war could hurt his chances of re-election too. Damned if he does, damned if he doesn’t.
Ever since tensions were ignited by the Hamas atrocities of 7 October and Israel’s response, there has been fear of widening conflict in the Middle East.
The president will try to calibrate his response so it punishes and deters but does not escalate.
But war is not a precise science. If US military action is disproportionately destructive it will demand a stronger response from Iran. A cycle of escalation will ensue.
Confrontation has been ratcheting up in the air, on land and at sea.
US and British airstrikes have followed attacks by other Iranian proxies, the Houthis, in the Red Sea. Attacks on US assets on the ground in Syria, Iraq and Jordan have intensified.
It is still assumed no one wants a much bigger war but events at some point may soon acquire an irreversible momentum, tipping the region into one.
That danger is far from receding, a moment of no return seems to be approaching with each passing day.