What the US and Iran do next could be even more momentous

The "tortuous" US-Iran relationship was tested at least once before, but this is of far greater magnitude

Watch LiveBritish Broadcasting CorporationHomeNewsSportBusinessInnovationCultureArtsTravelEarthAudioVideoLiveHomeNewsIsrael-Gaza WarWar in UkraineUS & CanadaUKUK PoliticsEnglandN. IrelandN. Ireland PoliticsScotlandScotland PoliticsWalesWales PoliticsAfricaAsiaChinaIndiaAustraliaEuropeLatin AmericaMiddle EastIn PicturesBBC InDepthBBC VerifySportBusinessExecutive LoungeTechnology of BusinessFuture of BusinessInnovationTechnologyScience & HealthArtificial IntelligenceAI v the MindCultureFilm & TVMusicArt & DesignStyleBooksEntertainment NewsArtsArts in MotionTravelDestinationsAfricaAntarcticaAsiaAustralia and PacificCaribbean & BermudaCentral AmericaEuropeMiddle EastNorth AmericaSouth AmericaWorld’s TableCulture & ExperiencesAdventuresThe SpeciaListEarthNatural WondersWeather & ScienceClimate SolutionsSustainable BusinessGreen LivingAudioPodcastsRadioAudio FAQsVideoLiveLive NewsLive SportHomeNewsSportBusinessInnovationCultureArtsTravelEarthAudioVideoLiveWeatherNewslettersWatch LiveAn unprecedented moment - but what the US and Iran do next could be even more momentous2 days agoShareSaveLyse DoucetChief international correspondentShareSaveBBCFor decades, the United States and Iran have carefully avoided crossing a dangerous red line into a direct military confrontation.

One American president after another held back from deploying their military might against the Islamic Republic for fear of sinking the US into potentially the most perilous Middle East war of all.

Now, the commander-in-chief, who promised to be a president of peace, has crossed this Rubicon with direct military strikes on Tehran's nuclear sites – the most consequential move yet in the second term of a president who has prided himself on breaking all the old rules.

It's an unprecedented moment provoking alarm in capitals the world over.

Iran's next move could be even more momentous. Its 86-year-old supreme leader Ayatollah Ali Khamenei, now reported to be sheltering in a bunker, has spent nearly four decades cautiously playing a long game against his most powerful enemy to protect his most important asset – the Islamic Republic.