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No meeting between a British prime minister and a US president would be complete without some transatlantic agonising about the state of the "special relationship".

David Cameron and Barack Obama will today try to head that off with both words and pictures.

the two leaders write of a relationship which is not just special but "essential - to our nations and the world... a partnership of the heart, bound by the history, traditions and values we share".

If that's not enough to silence the doubters the prime minister will later this evening become the first foreign leader to be welcomed aboard Air Force One by President Obama.

The two men will head to Ohio - a crucial swing state - to watch a game of basketball. The truth is that they need each other to face a daunting international agenda over the year ahead.

They'll discuss plans for what they call "the next phase of the transition" in Afghanistan - in other words the gradual withdrawal of troops over the next two years. They are promising to "continue to tighten the noose around (Syrian President) Assad and his cohorts".

Perhaps the most significant conversation will, though, be about Iran. Publicly they write about there being "time and space for a diplomatic solution".

Privately they will want to discuss what to do if Israel is set on war.