(Bloomberg) -- Prime Minister Boris Johnson will land in the U.S. on his first trip outside of Europe since the start of the pandemic with his most critical relationship -- with President Joe Biden -- at a delicate juncture.

A three-way deal to supply nuclear submarines to Australia announced this week has reinforced the idea of a special bond, underpinned by U.S.-U.K. security interests, even though the two men have not always seen eye to eye.

Johnson now has a number of other tricky topics with which he needs help from the U.S., including the crisis in Afghanistan and, especially, how to accelerate momentum behind a stumbling global environmental summit that the U.K. will host next month. On Monday, the prime minister will use a breakout meeting at the UN General Assembly in New York to urge wealthy nations to stump up more cash to fight climate change. 

He will then head to Washington for a meeting with Biden that will come under close scrutiny -- not only because of the U.K. media’s obsession with the “special relationship” immortalized by Margaret Thatcher and Ronald Reagan in the 1980s. There’s also the ghost of Donald Trump, who openly admired Johnson but humiliated his predecessor Theresa May. 

New Reality

Johnson’s relationship with Biden has so far been more awkward. He was rebuked by the president for endangering the Northern Ireland peace process with his approach to Brexit, and meaningful negotiations on a trade deal have yet to begin. Meanwhile the U.K. was left blindsided by the U.S. handling of the chaotic exit from Afghanistan amid little consultation with NATO allies.

With few opportunities for face-to-face meetings during the pandemic, the Conservative British leader has been unable to deploy his famous charm to win round the Democrat in the White House.

What’s clear is that close ties to the relatively new president and his team cannot be taken for granted, in spite of the history binding the two nations and Biden’s promise to international allies after taking office that “America is back.”

Read More: Even Without Trump Tensions Simmer Between the U.S. and Allies

In Afghanistan, for example, Biden rejected calls from the U.K. among others to delay the pullout of troops. And British officials have struggled to shift the Biden administration’s skepticism over Brexit.

Yet the U.S. seems more aligned with the U.K. over China than other European nations, a position underlined by the tightly-held secret that Australia was going to ditch France and attach itself to Biden and the U.K. in getting new submarines equipped with nuclear technology.

Diplomatic Spat

An angry France responded by pulling its U.S. envoy to Washington for the first time ever after being blindsided by the pact Biden, Johnson and Australia’s Scott Morrison discussed at the Group of Seven summit in England in June.

Yet Johnson must still tread carefully with Biden; there’s little sign of progress on his prized post-Brexit trade deal with Washington, while in the short term he needs the president’s support to secure more ambitious global climate pledges at the COP26 round of UN talks in Glasgow starting late October.

Both leaders spoke at a virtual meeting on Friday convened by the U.S. president on climate change, with Biden calling for nations to bring their “highest possible ambitions” to the Glasgow summit.

The U.K. is focused on delivering on the promise made at the 2009 summit in Copenhagen, and renewed in Paris in 2015, that poorer nations were to receive $100 billion per year from 2020 to help them cut carbon emissions. But wealthy nations are stalling in their efforts.

‘Small Window’

“World leaders have a small window of time left to deliver on their climate commitments ahead of COP26,” Johnson said in a statement ahead of his trip. “My message to those I meet this week will be clear: future generations will judge us based on what we achieve in the coming months.”

Biden’s stance will be critical to persuade others to follow suit, which is why Johnson’s mission is a delicate one and will rely on powers of persuasion.

Read More: Key Climate Talks Are Headed for Trouble After G-7 Wrangling 

But he’s fallen short before in negotiations on climate change: at the G-7 meeting in June, a deal to end domestic coal use in G-7 economies was scuppered over U.S. nervousness about the impact on domestic politics.

During those talks, he was working an the submarine alliance during private meetings. This week he’ll get a sense of how far that deal has helped to cement this crucial relationship. 

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