WASHINGTON (NYTIMES) - He heard from his generals and his diplomats. Lawmakers weighed in and so did his advisers. But among the voices that rang powerfully for United States President Donald Trump was that of one of his favourite Fox News hosts: Tucker Carlson.

While national security advisers were urging a military strike against Iran, Mr Carlson in recent days had told Mr Trump that responding to Teheran's provocations with force was crazy. The hawks did not have the president's best interests at heart, he said. And if Mr Trump got into a war with Iran, he could kiss his chances of reelection goodbye.

However much weight that advice may or may not have had, the sentiments certainly reinforced the doubts that Mr Trump himself harboured as he navigated his way through one of the most consequential foreign policy decisions of his presidency. By his own account, the president called off the "cocked & loaded" strike on Thursday night with only 10 minutes to spare to avoid the estimated deaths of as many as 150 people.

The concerns that Mr Trump heard from Mr Carlson reflected that part of the presidential id that has always hesitated at pulling the trigger. Belligerent and confrontational as he is in his public persona, Mr Trump has at times pulled back from the use of force, convinced that America has wasted too many lives and too much money in pointless Middle East wars and wary of repeating what he considers the mistakes of his predecessors.

As Mr Carlson and other sceptics have argued, a strike against Iran could easily spiral into a full-fledged war without an easy victory. That, Mr Trump was told, was everything he ran against. And so the president struggled into the early evening, committed to taking action to demonstrate resolve right up until the moment he decided against it and called off the warplanes and missile launchers.

"To those who want to criticise the president, I would say they ought to be thankful they're not the ones having to make that decision," said Senator Jim Risch, a Republican from Idaho, the chairman of the Foreign Relations Committee, who was among the lawmakers at the White House that day.

"I watched him really agonise over this."

The full story of how Mr Trump set in motion an attack on another country and then cancelled it remained to some extent shrouded in mystery even to some of those involved, according to interviews with administration officials, military officers and lawmakers, many of whom asked not to be named. On the day after the aborted strike, multiple, seemingly conflicting accounts emerged and the White House made no effort to reconcile them, choosing to stay silent about the deliberations. A spokesman for Fox News declined to comment.

One thing made clear yet again, however, was just how different Mr Trump's decision-making process is from those of other presidents, even on the weightiest of issues to confront a commander in chief.

Meetings and memos aside, he trusts his instincts more than institutions, reaches out to unconventional sources of guidance and is willing to defy a roomful of advisers. He has not had a Senate-confirmed defence secretary for nearly six months, and the acting secretary resigned this week. And those advisers he does have were busy trying to outmanoeuvre each other.

Mr Trump had been resisting a military response to repeated provocations by Iran for weeks by the time he woke up Thursday morning to discover that a US spy plane had been shot down. Now led by Mr John Bolton, his hawkish national security adviser, the president was faced with the choice of how to respond.

On Thursday morning, only hours after the drone was shot down, Mr Bolton met for breakfast at the White House at 7am with Mr Patrick Shanahan, the Acting Defence Secretary who had announced his resignation just three days earlier, as well as with Mr Mark Esper, the Army secretary set to replace Mr Shanahan, Secretary of State Mike Pompeo and General Joseph Dunford, the chairman of the Joint Chiefs of Staff.

The group discussed the drone episode and deliberated a possible military response to recommend to the president. At 11am, the same group along with other national security officials met with Mr Trump to brief him on options for a strike on Iran. According to one administration official, the potential casualties of such an attack were discussed at that meeting.

But as usual, Mr Trump did not rely exclusively on his official team. Among the outsiders he talked with in the morning was Senator Lindsey Graham, a Repubulican from South Carolina, a close ally. Mr Graham urged that he consider a military response to the drone's shooting down.

At 3pm, Mr Trump hosted congressional leaders in the Situation Room to brief them about the episode and outline the alternative responses. At least some of those in the room left assuming that he was likely to order a strike.

Mr Trump was given a list of at least a dozen strike options generated this month after there were attacks on tankers in the region. The list was then narrowed down to at least two alternatives. Among the targets would be facilities like radar and missile batteries.

Administration officials said on Friday that the president's national security team was unanimous in favouring a response and all agreed with the final option recommended to Mr Trump. But several military officials said General Dunford cautioned about the possible repercussions of a strike, warning that it could endanger US forces and allies in the region. A 6pm meeting in Mr Shanahan's office at the Pentagon including General Dunford was described as particularly tense.

As for Mr Pompeo, he argued during meetings at the White House that sanctions were having a powerful effect by slashing Iran's revenues from oil sales, according to a senior administration official familiar with the discussion. While he expressed support for a pinpoint military response, he stressed that the sanctions were having the long-term effect the administration had hoped. Some of Mr Trump's aides wondered whether a strike would upset a strategy that was already working.

As of 7pm, senior US officials were told the strike was on and would be carried out between 9pm and 10pm, or just before dawn in Iran. Within an hour, it was called off.

On Twitter and in an interview with NBC News, Mr Trump attributed his change of heart to a desire to avoid casualties.

"I want to know something before you go," he said he asked his generals. "How many people would be killed, in this case Iranians?" The generals, he said, replied that about 150 people would die.

"I thought about it for a second, and I said, you know what, they shot down an unmanned drone, plane, whatever you want to call it, and here we are sitting with a 150 dead people that would have taken place probably within a half an hour after I said go ahead," Mr Trump told NBC's Chuck Todd. "And I didn't like it, I didn't think, I didn't think it was proportionate."

But an administration official informed about the discussions privately disputed that account. The 150-dead casualty estimate came not from a general but from a lawyer, according to the official. The estimate was developed by Pentagon lawyers drafting worst-case scenarios that, the official said, did not account for whether the strike was carried out during daytime, when more people might be present at the targets, or in the dark hours before sunrise, as the military planned.

That estimate was passed to the White House counsel, Pat Cipollone, without being cleared with Mr Shanahan or General Dunford. It was then conveyed to the president by the White House lawyers, at which point Mr Trump changed his mind and called off the strike.

Pentagon lawyers are typically involved in casualty and collateral damage estimates, charged with considering the worst possible outcome. Such numbers are fluid and almost always a rough guess, as it is almost impossible to know who or what will be at the site of an attack when it occurs.

But the lawyers' involvement was seen by some of Mr Trump's aides as an attempt to circumvent Bolton to influence the president. In effect, whether intended to or not, the casualty estimate played to the concerns that Trump had shared with Carlson and other sceptics of military action in the Middle East.

General Jack Keane, a retired Army vice chairman who is close to the Trump White House, said another factor came into play during the deliberations - the president was told that the attack on the drone was really a mistake, as Mr Trump had publicly suggested to reporters early in the day.

"The president got some additional information that the Iranian national leaders were frustrated or furious with the tactical commander who made the decision to shoot down the American drone," General Keane said. Among those who were said to be angry, he said, was Qasem Soleimani, the powerful commander of Iran's elite Quds Force.

General Keane said it was unclear whether the commander who ordered the downing of the drone was operating within his authority or was a rogue figure. But either way, he said, it impressed upon Mr Trump that he would be risking a dangerous escalation over what was not intended to be an attack by Iran's top leaders.

"I don't think that's what was decisive for the president," General Keane said, but it contributed to the decision, which he said was mainly driven by the casualty concern. "What was decisive for him was the comparison for him, compared to destroying missile batteries and killing people, of shooting down a drone." By this point, time was running out. Mr Graham, who had pushed for a strike, was on an aeroplane heading to the West Coast and out of touch. Mr Trump scrubbed the mission.

The decision made, the military ordered ships and planes in the region to stand down. At the White House, Trump turned on his television to watch the opening of Carlson's 8pm show, where he heard what surely must have sounded like vindication. On screen, Mr Carlson declared that "foreign wars have ended in dismal failure for the United States". While no decision had been announced yet, Mr Carlson praised Mr Trump for resisting military intervention in Iran.

"The same people who lured us into the Iraq quagmire 16 years ago are demanding a new war, this one with Iran," he said.

"The president, to his great credit, appears to be sceptical of this - very sceptical."

If he kept the television on, though, Mr Trump would have heard a radically different message from another friend on Fox at 9pm. With the news of Mr Trump's decision still not public, Mr Sean Hannity declared that Trump may have "no choice" but to "bomb the hell out of them". For one night, at least, that would not be true. But the battle for Mr Trump's ear is not over.