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. This time, an internal upheaval is compounded by an external threat, as President Trump's warnings of military action come after the US carried out strikes on key nuclear facilities during a 12-day war between Iran and Israel. Although Trump claims Tehran has shown interest in negotiations, the Iranian leaders remain steadfast, unwilling to meet maximalist demands. Meanwhile, the Iranian populace faces a severe economic crisis, leading to increased unrest and violent crackdowns. The current moment in Iran may ultimately determine whether protests will lead to significant change or harsh repression.