Iran's rulers are confronting their most serious challenge since their own 1979 revolution.
They're now countering on an unprecedented scale - a ferocious security crackdown and near-total internet shutdown has been unleashed on a scale unseen in previous crises.
Some of the streets once engulfed by a roar of anger against the regime are now starting to go silent.
On Friday it was extremely crowded - the crowd was unbelievable - and there was a lot of shooting. Then Saturday night it became much, much quieter, a resident of Tehran told BBC Persian.
You would have to have a death wish to go out now, one Iranian journalist reflected.
This time, an internal upheaval is also compounded by an external threat, with President Trump's repeated warnings of military action coming seven months after the US carried out strikes on key nuclear facilities during a 12-day war between Iran and Israel, which left the regime weakened.
But, to use an analogy often used by the American leader, that has also given Iran another card to play.
Trump now says Tehran has called to go back to the negotiating table.
But Iran doesn't have a good hand: President Trump says he may still have to take some kind of action before any meeting; talks won't take all the searing heat out of this unrest.
And Iran won't capitulate to what have been the US's maximalist demands, including zero nuclear enrichment, which would cross red lines that lie at the very heart of this theocracy's strategic doctrine.
Whatever the pressure of this moment, there's no sign Iran's leaders are changing course.
Their inclination is to clamp down, to try to survive this moment, and then to figure out where they go from here, says Vali Nasr from the Johns Hopkins School of Advanced International Studies, author of the book Iran's Grand Strategy.
But given their straits with the US, with Israel, with sanctions, even if they quell these protests, they don't have many options to improve the lives of Iranians.
This week may decide the momentum in this moment - whether Iran and the wider region are plunged into another bout of military attacks; whether brute force has completely put down these protests – as it has in the past.
Iran's Foreign Minister Abbas Araghchi told diplomats in Tehran today that the situation is now under total control.
Outside, in the bright light of day, the streets of Tehran were filled with the crowds the government called on to come out and reclaim the streets from protesters.
Five days into a comprehensive communications blackout, a more chilling picture still sneaks out into the world through Starlink satellite terminals, Iranian technical creativity, and courage.
Doctors' accounts of hospitals overwhelmed by casualties, grim videos of open-air mortuaries dotted by long lines of black body bags, voice notes sent to journalists at the BBC Persian Service expressing shock and fear.
The numbers rise. In the last wave of unrest in 2022 and 2023, which lasted more than six months, around 500 deaths were recorded by human rights groups and more than 20,000 arrests. This time, within a few weeks, reports say the death toll already climbs far higher and more than 20,000 have been taken in so far.
The government doesn't deny the bloodshed; state TV is also airing images of makeshift mortuaries, even admitting some protesters have been killed.
The streets of Iran have been on fire. Government buildings have been set alight as anger burned. They are symbols of the system, but attacks on public property are condemned by the government as the work of terrorists and rioters.
Legal language has also hardened in this time - vandals will be charged with waging war against God and face the death penalty.
The government puts the main blame on foreign enemies - a code name for Israel and the US - for an internal upsurge. This time, their accusation is also fuelled by the clear extent of infiltration by Israel's Mossad security agency during their 12-day war last year.
With every new eruption of unrest in Iran, the same questions are asked: how far and wide do these protests reach; who's taking to the streets and squares; how will the authorities respond?
