The ceasefire in the Gulf is four weeks old and showing its age. The US and Iran's determination to keep the pressure on each other has put it in serious jeopardy. This is a dangerous moment.
The ceasefire opened up a chance for diplomacy that looked for a short time as if it might make progress. Americans and Iranians faced each other across a conference table in Pakistan's capital, Islamabad, but came away empty-handed.
The Pakistanis are trying to revive the process, without much success so far. Both America and Iran want to have a deal. But they have different deals in mind and are sticking to their red lines. Until one or the other, or preferably both, decide to offer concessions, renewed full-scale hostilities remain an incident away.
More than ever there is a strong risk of misperception and miscalculation of intentions and consequences. Both are classic ways in which crises slip out of control and wars escalate.
America's decision to escort two ships through the Strait of Hormuz was always going to produce a reaction from Iran. This week's urgent question is whether it ends there or whether more action and reaction power a slide back into all-out war.
Control of the Strait of Hormuz has become the central issue in the crisis. It was open to navigation, without restriction or the payment of tolls, until 28 February -when the US and Israel attacked Iran. Now Iran has demonstrated how closing it can mean everything from an offensive weapon to a revenue raiser and an insurance policy. This week, Iranian Foreign Minister Abbas Araghchi has told MPs that there will be no return to the old status quo.
The US cannot allow Iran to make the Strait of Hormuz into home waters that the Tehran regime can control and use to charge shippers millions in tolls, without accepting that tactical victory over Iran's armed forces has become a strategic defeat.
Closing the strait has global economic consequences. The length of time it stays closed will determine how severe the consequences of the war will be for people across the world. Shortages of oil and gas, as well as helium for high tech industries and feedstocks for fertiliser, are having an increasingly heavy impact on millions of people a long way from the war zone. The fertiliser crisis risks causing hunger in countries that do not have secure food supplies.
President Donald Trump's motives, declared and undeclared, are always complex and changeable. He has used social media to try to persuade oil traders not to drive up the price of petrol for American motorists.
He must also be frustrated by the Iranian regime's resilience and determination to resist however much pain America and Israel inflict on the country. A regime prepared to shoot its own citizens in the streets for protesting, as the Islamic Republic's security forces did once again in January, is not going to worry too much about their welfare - at least not until it affects their hold on power.
Trump's frustration is the result of his own rash decision to go to war assuming an easy victory, without thinking through the consequences of what happens and what to do if it isn't easy. The US has shown the power of its highly efficient military, but the president's fluctuating decision-making has left the country in a strategic bind.
Trump's decision to order the US Navy to escort a couple of ships through the strait does not restore freedom of navigation. An average of 138 ships passed through the strait each day until the US and Israel went to war, according to the Joint Maritime Information Centre.
Iran has shown that it is prepared to go back to war and might even be prepared to set the pace of escalation. It is strategy full of risk, but for the men who have replaced the former supreme leader and all the senior leaders killed by the US and Israel, it is a risk worth taking.
The United Arab Emirates (UAE) looks to be the main target for Iran among their Gulf Arab neighbours. In response, the UAE has doubled down on its alliances with the US and Israel. The Israelis sent an Iron Dome anti-missile system to the UAE, and IDF soldiers to operate it – a significant gesture they refused to offer to Ukraine.
Iran's decision to target the Emirati port of Fujairah is significant. It is on the UAE's small stretch of coastline that is beyond the Strait of Hormuz, facing instead the Gulf of Oman.
Fujairah is the terminus of an oil pipeline that allows the UAE to export without going through Hormuz and has big oil storage facilities. That makes it strategically and economically vital for the Emiratis. They are deeply concerned about Iran's next moves. Despite robust public warnings to Tehran, and capable armed forces, the Emiratis still prefer to stay out of direct attacks on Iran. That policy might not survive a collapse of the ceasefire. Longer term, it is spending more billions on American weapons.
Trump seems still to believe that the Iranian regime will buckle in the face of US pressure and military force. He would like to be able to flourish a deal, but he will not accept one that his critics would say was not as good as the nuclear agreement that became President Barack Obama's signature foreign policy achievement.
During his first term, Trump dumped that agreement, known as the JCPOA, with substantial encouragement from Israel's Prime Minister Benjamin Netanyahu. He replaced it with a policy he called "maximum pressure" that failed to stop Iran enriching uranium and now looks to have started America and Iran on the road to a war that has no easy exits.
Correction 6 May: An earlier version of this article said 40 to 60 ships passed through the Strait of Hormuz each day before the war. In fact, an average of 138 vessels travelled through the strait daily before 28 February, according to the Joint Maritime Information Centre. This article has been amended to reflect that figure.
