When John Kerry was US secretary of state during the second term of the Obama administration, his deputy was Antony Blinken, a Washington veteran steeped in the foreign policy establishment.
Now Mr Kerry is coming back into government as special presidential envoy on climate change, a role in which he will be subordinate to Mr Blinken, who has been picked by president-elect Joe Biden as secretary of state.
Mr Blinken’s seniority to his erstwhile boss could create an unusual power dynamic: if the relationship were to become fraught, it would threaten to undermine Mr Biden’s effort to put climate change at the forefront of his foreign policy agenda and combat what he has described as “one of the most pressing threats of our time”.
Any rancour between the pair could also complicate the Biden administration’s attempt to improve the standing of the US on the world stage as it seeks to unwind the isolationism of Donald Trump’s presidency.
“It’s an atypical relationship,” John Podesta, former counsellor to Barack Obama and a climate advocate, told the Financial Times, although he insisted the pair would find “a modus operandi to work together”.
As secretary of state in the second term of the Obama administration and a former chairman of the Senate foreign relations committee, Mr Kerry drew criticism for what some saw as his outsized ego and the belief in his personal ability to forge powerful relationships to resolve fraught global problems.
But Mr Kerry, who unsuccessfully ran for president against George W Bush in 2004, is also seen as an optimistic centrist with a long-held interest in tackling climate change who likes to build alliances.
“Kerry will be the ‘secretary of world’ and Blinken will be the secretary of state,” quipped Kevin Book, managing director at the ClearView Energy Partners consultancy, adding that Mr Kerry would relieve Mr Blinken from covering the climate portfolio.
Mr Book said Mr Kerry was “a shoo-in for the job” because he helped negotiate the 2015 Paris Agreement to limit global warming, which the Trump administration withdrew from.
Mr Kerry will spearhead not only America’s return to the deal on the first day of the incoming administration but efforts to strengthen it. He is expected to push other countries to adopt more ambitious domestic climate targets, whether transitioning from coal to clean energy or clamping down on methane emissions.
There is little doubt that Mr Blinken is the most senior of the pair: he will be the first cabinet member in the presidential line of succession behind Kamala Harris, the vice-president, and two others.
Yet Mr Kerry, who will carry the rank of cabinet member, has been afforded a level of prestige that is unusual for a presidential envoy. He will attend White House meetings with fellow national security principals, an arrangement designed to make climate change — and Mr Kerry — central to US foreign, security and economic policy.
Mr Kerry might also be given an office on the lavish seventh floor of the department, which is normally reserved for top officials and the secretary of state, according two people briefed on the arrangements. And if he is on an overseas trip designated as a presidential mission, he an his team may be eligible to travel by US military aircraft.
A spokesman for the Biden transition team said it would “be premature for us to weigh in on logistics at present” when asked about office and plane arrangements.
Mr Kerry is also likely to meet heads of state who are senior to the foreign ministers that Mr Blinken will often work with. “Kerry is the kind of guy who will see presidents and prime ministers, not the energy minister,” said Mr Podesta.
Mr Kerry told NBC News last week that he respected and understood “the lines that are drawn within the state department and the administration”, in response to concerns that world leaders might reach out directly to the better-known Mr Kerry rather than Mr Blinken.
Friends and colleagues describe Mr Blinken as a laid-back professional who will be confident he has the president’s ear, but his role may be complicated by the presence of his former boss.
“Any time you have a former secretary of state playing a big, overlapping role with the current . . . there’s bound to be some risk of tension between them,” said Jeff Colgan, director of the Climate Solutions Lab at Brown University.
Kelly Sims Gallagher, former climate adviser to Mr Obama, said the challenge would be determining the level of priority accorded to climate issues within foreign policy.
“How is climate integrated in regional strategies and policies? How does climate rank in importance in terms of lists of priorities for bilateral relationships?” she asked.
By putting climate change at the forefront of his foreign policy, Mr Biden has set the stage for Mr Kerry to wield outsize influence in areas beyond his remit.
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For instance, Mr Biden’s team is already asking what role Mr Kerry will play in setting China policy. Republican and Democratic Asia experts — who want the administration to take a tough stance towards the country — worry Mr Kerry is not hawkish enough on Beijing and that he might argue against aggressive action on issues such as human rights in order to secure climate deals.
“Kerry will want to go to Beijing very early on. He will want to prioritise progress on climate over most other things in the US-China relationship,” said one former Obama administration official.
Managing Mr Kerry’s approach to China would, he added, be “one of the biggest challenges for” Mr Blinken.