After a diplomatic team led by US Vice-President JD Vance tried, and failed, to reach a negotiated agreement to end the war with Iran on Saturday, President Donald Trump had to decide his next move.

That came on Sunday morning, in a series of Truth Social posts.

The US will impose a naval blockade of Iran, he wrote. "No one who pays an illegal toll will have safe passage on the high seas," he wrote.

He also said that the US would continue clearing mines from the Strait of Hormuz to ensure a safe passage for allied shipping. The US military, he added, was "locked and loaded" and prepared to resume attacks against Iran at an "appropriate moment".

He went on to say that while progress had been made in the 20-hour negotiations in Islamabad, Iran would not meet the US demand that it abandon its nuclear ambitions.

That view was contradicted somewhat by a US official familiar with Vance's negotiations, who spelled out a much longer list of disagreements – including on Iran's control of Hormuz and its support for regional proxies, like the Houthi rebels in Yemen and Hezbollah in Lebanon.

While Trump's latest posts didn't have the apocalyptic bluster of last week's threat to end Iranian civilisation, they pose a number of new challenges – and risks – for the American side.

Will mine-clearing activities place American naval vessels at greater risk of Iranian attacks? How would the US determine who paid Iran a toll? Will the US use force on foreign-flagged ships that ignore the blockade? How will nations that depend on Iranian oil, like China, respond? Will the move, intended to choke off Iran's primary income stream, drive the price of oil to even higher levels?

There are no clear answers.

Later on Sunday, the US military Central Command announced that the naval blockade would stop all ships travelling to or from Iranian ports – a different set of conditions than in Trump's earlier proposed action.

"I don't understand how blockading the strait is going to somehow push the Iranians into opening it," Senator Mark Warner of Virginia, the ranking Democrat on the Senate Intelligence Committee, told CNN on Sunday.

On CBS' Face the Nation programme, Republican congressman Mike Turner of Ohio, who until last year chaired the House Intelligence Committee, said the blockade was a means to force a resolution to the situation in Hormuz.

"The president, by saying we're not just going to let them decide who gets through, is certainly calling all of our allies and everyone to the table," he said. "This needs to be addressed."

He could continue to ratchet up the US attacks on Iran, possibly doing long-term damage to the nation's civilian infrastructure, adding to a humanitarian crisis and further destablising the global economy.

Or, he could back away from a war that has always been unpopular among the American public and is beginning to frustrate even some of Trump's supporters, who believed his promises to avoid extended foreign conflicts and Middle East entanglements.

A new CBS poll suggests that most Americans (59%) feel the war is going somewhat or very badly for the US.

Many believe the key US objectives - such as keeping open the Strait of Hormuz, securing greater freedom for the Iranian people and permanently ending Iran's nuclear programme - remain unmet. Overwhelming bipartisan majorities feel it's important for the US to achieve these goals.

Nearly a week has passed and, despite American claims of victory, the predicaments facing the president have not changed.

Trump told Fox News on Sunday morning that Iran would ultimately give the US "everything" it wants. He added that while oil prices might be the same or higher in the months ahead, he believed the US economy would hold up.

That, to say the least, is a gamble.

And with November's midterm elections looming, the president's Republican Party could pay dearly at the polls if he is wrong.

On Saturday night, as his vice-president was negotiating with the Iranians in Pakistan, Trump travelled to Miami, where he watched prize fighters batter each other in UFC cage matches.

It was, according to members of the press pool in attendance, a bizarre spectacle.

The president of the United States observed violent contests in a blood-spattered ring, chatted to celebrities and, at times, engaged in intense discussions with his Secretary of State Marco Rubio and other advisers, in full view of the thousands of attendees.

Ultimate fighting cage matches, despite their ferocity, have set rules and time limits, and end with a clear winner and loser.

It's the kind of clarity that the Iran war may never provide, as it stretches into its second month and the current two-week ceasefire appears on the verge of collapse.

The conflict has become a test of wills – of Iran's ability to endure continued US and Israeli attacks versus Trump's tolerance for the economic and political pain the war has produced.

In the end, all the participants in this fight might be diminished.