For a prime minister who has spent a year focusing on building a warm rapport with the US president, using the authority of the despatch box at Prime Minister's Questions to declare that he "will not yield" was a big moment.

It was a tonal shift even from Monday's speech in Downing Street.

No wonder, given the tirade unleashed by President Trump in Sir Keir Starmer's direction on his Truth Social platform in the early hours of Tuesday morning.

Behind the scenes, Sir Keir had been coming under greater pressure to change his approach to the president.

"It is a strategy that has failed on every conceivable level," one Labour MP said in the hours before PMQs, warning that their constituents were increasingly frustrated by the prime minister's attempts to build a rapport with Trump.

"It gets harder and harder to hold your head up high when you're campaigning," the MP said.

One minister said they were concerned that history may not judge Sir Keir's approach kindly.

"This is not just about how it looks now," they said. "In five years time will we look back at this approach and see it as appeasement? See it as a massive error?"

Several Labour figures say privately they believe that the prime minister ought to follow the example of Mark Carney, the Canadian prime minister, who warned in a speech at the World Economic Forum in Davos on Tuesday that the "old order is not coming back".

He said: "Middle powers must act together because if we're not at the table, we're on the menu."

Carney's problems with the US are more acute than the UK's.

In the moments before his post on Truth Social accusing Sir Keir of "stupidity", Trump posted a map of the US which incorporated not only the US but Canada too, as well as Greenland and Venezuela.

Trump appearing to revive his threats towards Canada could pose particular problems for Sir Keir, too.

At the heart of Sir Keir's strategy for handling Trump - a strategy which was seen until this week as one of the clearest triumphs of his time as prime minister - was the use of the Royal Family.

On his first visit to the Oval Office to meet Trump last year, Sir Keir whipped from his pocket a letter from the King extending an invitation to Trump for an unprecedented second state visit to the UK.

That has now happened but it does not seem to have secured permanent warm relations with Trump.

And the King is the King of Canada as well. What does the deterioration in US-Canadian relations mean for the expected visit of the King to the US this year to mark 250 years of its independence?

Even as his position toughened rhetorically today, those around Sir Keir remain resistant to pressure for him to deliver the full-throated 'Love Actually moment' some in Labour desire.

"You can have these fantasies about sticking it to world leaders," one confidant of the PM said, "but you still have to speak to them the next day. What do you say then?"

It seems likely that Sir Keir's rhetoric in PMQs will sate some Labour MPs for now.

But there was a warning from Steve Witherden, a backbencher from the left of the Labour Party, that there will be ongoing pressure for him to go further: Witherden urged retaliatory tariffs on the "thug in the White House" - an approach the prime minister is desperate to avoid.

The government can take heart, in the circumstances, that Trump's retraction of his previous endorsement of the Chagos deal appears to be based on at least two false premises.

Speaking in the White House on Tuesday evening, he seemed to suggest that the terms of the deal had changed significantly since it was commended by Marco Rubio, the secretary of state, in May. That is wrong.

He also suggested that the UK was doing it for the money, which does not make sense as one of the most notable features of the deal is that the UK is paying Mauritius to lease Diego Garcia, where the US-UK military base operates, for the next 99 years.

Parochial as it sounds, some Labour MPs fret about where this leaves them politically here in the UK, especially in the run-up to the local elections where Labour faces a threat to its left from the Greens, and in other areas from the Liberal Democrats, who have been questioning Sir Keir's approach to Trump for months.

One government source observed that a key Labour attack line on the Greens is that they have advocated leaving the Nato alliance. What power does that attack have, the source asked, when Trump's actions call into question the existence of Nato anyway?

Others in Westminster are concerned attempts to calm the geopolitical tensions are being hampered by the seeming lack of skilled ambassadors in either capital.

Investment banker and Trump donor turned diplomat Warren Stephens seems to be keeping a notably low profile as the US's man in London.

"Where on earth is he?" asked one Labour MP. "He's completely absent and seemingly well out of his depth.

"No appearances on the broadcast round, no engagement with Parliament, no broadsheet coverage, not on the airwaves, zero mention of Greenland or Chagos on his Twitter account. I'm livid."

Stephens may be finding out - as the sidelined special envoy to Ukraine Keith Kellogg did - that with President Trump, big job titles do not necessarily signify big influence.

And more than four months after Lord Mandelson was sacked as the UK's ambassador to Washington, a permanent replacement is still not in place.

Foreign Office veteran Christian Turner is awaiting the formal acceptance of his nomination from the US State Department. He is also understood to be in the process of moving with his family to the states.

All these issues present Sir Keir with important choices.

While the prospect of an imminent threat to his leadership appears to have receded in 2026, he cannot afford for Labour MPs to turn on him over his handling of foreign affairs - an area where many still give him great credit.

"Their whole strategy for handling the PLP [Parliamentary Labour Party] has been about his management of international crises," one Labour MP said.

"If he doesn't have that, what does he have?"