Donald Trump shared the post as if nailing a threat to the door: if the Islamic Republic began to massacre its people, he vowed, America was 'locked and loaded and ready to go'.

It was a stark – and welcome – contrast to the limp words that then-President Barack Obama offered during the 2009 Iranian uprisings. As regime forces butchered people with promiscuous abandon, Obama had pursed his lips and admonished the mullahs.

'The world is watching,' he said, disapprovingly.

Obviously, it made no difference.

Trump has made his stance clear. Yet now the time has come to prove whether his rhetoric was mere bluster or an actual pledge.

Because on Saturday the mullahs did what they always do when they plan to spill blood: they cut the country's communications, choking the protesters by severing the fibre-optic cables. Iran went into a near-total digital blackout.

I realised almost immediately from the sudden silence of people inside Iran who had been speaking to me.

Chats previously humming with updates, gallows humour and gossip suddenly went dead.

Debris burns outside a religious centre in the city of Gorgan

Clearly this was no 'technical issue'. It was a state act and an order from the very highest levels.

Soon the news was global and even Amnesty condemned it. (Spare a thought for their poor activists, no doubt distraught at having to condemn a fanatical Islamist regime)

This is the Islamic Republic's modus operandi. Cut the light, then swing the truncheon, block the footage and bury the dead.

But even through the blackout, scraps of video and testimony are dribbling out: footage of regime thugs firing live rounds, bloodied bodies in the dirt.

The opposition channel Iran International reports claims of mass casualties and security forces using live fire; other outlets describe the same grim arc.

This is the culmination of Iran's long cycle of protests – but now the demands have changed irretrievably. Once, the protesters chanted for reform. About loosening the veil. About votes, rights – 'woman, life, freedom' (Zan, Zendegi, Azadi), they roared.

That's over. The people now want the regime gone.

Nothing less will do.

A system can survive protests that demand better treatment. It can't survive a mass movement that asks for its head. The mullahs' downfall is inevitable, even if not necessarily imminent.

Don't believe me? Consider the image that has become a shorthand for these protests. A young woman