All-out war, or not, in the Middle East? Biden's test at the most dangerous moment

“What next?” It’s a question anxiously asked too many times in the past six months.

And no doubt the question formed the crux of the late-night call between President Biden and Prime Minister Netanyahu.

Follow live: Iran launches attack on Israel

Iran’s spectacular drone and missile assault on Israel is truly unprecedented.

A region already reeling from the Hamas attacks and the Israeli retaliation on Gaza is being rocked again.

American leadership and leverage, tested repeatedly, is undergoing a bigger strain still.

This time though the consequence of President Biden’s test is all-out war, or not, in the Middle East. It is the scenario most feared since 7 October.

Without question, this moment – right now – is the most dangerous yet, by a long way.

A direct attack by Iran, from Iranian soil, against Israel is a red line crossed in Tel Aviv.

Iran’s trigger was another unprecedented moment and another red line crossed, on 1 April, when a missile landed on the Iranian consulate in Damascus, Syria killing 16 people. The Israeli trigger for that? Iran’s malign regional behaviour, as they would see it.

Tit, tat, tit, tat. You can see how this spirals. It explains the grim faces of the US president and his officials in the White House situation room overnight.

Even though so many of the drones and missiles were intercepted and despite no mass casualty scenario, Israelis will feel profoundly vulnerable, and the Israeli government may feel compelled to retaliate.

Impressions and the re-establishment of deterrence count for a lot in the Middle East.

That is precisely why Iran hit back after the Damascus consulate attack. It’s also why Israel may be unable to ignore Tehran’s weekend wave of drones and missiles. Never in its history has Israel faced an aerial assault like this.

And of course, in the White House they know all this all too well. But we all know too that the US-Israeli relationship has been severely strained by Gaza.

President Biden’s test now is to balance the action and reaction of a nation facing a moment that will feel, internally, to be existential with the consequences of an all-out regional war.

Significant Jewish settler violence in the West Bank, Hezbollah attacks from southern Lebanon and the continued disaster in Gaza all risk compounding the chaos.

Iran’s actions were more than anyone had expected. An unprecedented and enormously risky attack on Israel. It was an extreme attempt to re-establish deterrence. That works both ways.

Just six months ago, days before 7 October, President Biden’s national security advisor Jake Sullivan wrote “the region is quieter than it has been for decades… We have de-escalated crises in Gaza & restored direct diplomacy…”

He was spectacularly misguided.