Aukus deal: Summit was projection of power and collaborative intent

This was an occasion when old democracies came together to counter a new and growing adversary - China

This was a projection of power and collaborative intent in images and words.

Under warm early spring sunshine the message was clear.

The imagery and words working in unison: old democracies coming together to counter a new and growing adversary - China.

The submarines deal will create thousands of jobs in Barrow-in-Furness in Cumbria, in Derby and elsewhere.

And while any political agreement can be unpicked by successors, the budgets, decades-long timelines and near inevitability of China's strategic importance suggest this is an alliance that could last.

The trip rounds off an intense blast of international diplomacy for Rishi Sunak, after Friday's dash to Paris.

The prime minister's team appear happy with how it went, although being described in public by US President Joe Biden as a man who "has a home here in California" is not an element of his biography they would seek to put up in lights.

He faced questions too on this trip - not least from me - about a story in The Guardian he doesn't deny, that the electricity grid in his corner of North Yorkshire had to be upgraded, at his own expense, to provide the power needed to heat his private swimming pool.

There is no suggestion of any scandal. It is, instead, a further illustration of his vast wealth. It is for you to decide whether this matters one iota, or not.

Some of his political opponents seek to use it to suggest a detachment from the day-to-day worries of millions of families. Others are squeamish about sounding envious or anti-aspiration.

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This trip also taught us about some future moments to look ahead to. One firmly in the diary. The other almost firmly in the diary.

"It's my intention to go to Northern Ireland and the [Irish] Republic", said President Biden, referring to the 25th anniversary of the Good Friday Agreement in April.

It's thought he will formally confirm his plans on St Patrick's Day, when many of Northern Ireland's politicians will be in Washington.

And talking of Washington, the prime minister will head there in June.

This trip to California was Rishi Sunak's first to the US as prime minister, but its focus was narrow, on defence. The aim of the visit in the summer would be to discuss a far wider range of issues.

Now, as I type these words on the flight back from San Diego, attention turns back to the domestic fray - and Wednesday's Budget.