The email, sent to some members of the Clinton campaign’s inner circle, including campaign chairman John Podesta, not only revealed how Beijing is communicating with the candidates through the usual diplomatic backchannels, but also allowed the public a rare glimpse into the famously guarded inner workings of Clinton’s team of advisers.

The four other recipients of the email were senior Clinton foreign policy advisers Jake Sullivan and Laura Rosenberger, speech-writer Dan Schwerin and Daniel Kurtz-Phelan, a State Department policy planner during Clinton’s time as secretary of state, who helps Rosenberger coordinate with the multitude of other Clinton advisers.

Diplomatic sources in Beijing and Washington have confirmed that Beijing, aware of the high stakes for bilateral ties, has been following the election campaign closely and trying to maintain regular contact with both candidates, Clinton and Republican nominee Donald Trump, through their campaign teams and other channels.

One of the main assignments for China’s diplomatic mission in the United States has been to establish contacts with Clinton advisers and gauge their views in a bid to prepare for dealings with the next US administration, given that Clinton has long looked likely to win the White House race.

“We’ve had good communications with Clinton’s team, largely through [incumbent and former officials of] the Barack Obama administration,” said one Chinese diplomat who requested anonymity.

A former US ambassador to Beijing, Stapleton Roy, said that during election seasons, career diplomats were often tasked with the challenging job of keeping track of major candidates and their key advisers.

“With Clinton, we at least have the ability to guess what her policies will be,” Roy said. “And we also have the sense of who the people around her will be, whether it’s Kurt Campbell, or [former deputy secretary of state] James Steinberg, people of that sort, we have some idea where they stand on issues.

“But with Donald Trump you don’t have any of these. He has no track record on diplomacy at all.”

Observers note that Clinton has a vast network of foreign policy experts – a mixture of long-time Clinton aides and newer professionals – which could be one of her biggest assets if she is elected US president on Tuesday.

The inner circle of her advisory team includes many seasoned diplomats and national security specialists, some of whom served in the administration during the eight years from 1993 that her husband Bill was US president. Others were at the State Department during the four years that she was secretary of state, in Obama’s first term, or were members of the wider Obama administration.

The Council on Foreign Relations, a New York-based think tank, describes Clinton’s star-studded line-up as “a brain trust of internationalists confident in the use of American power but also cognizant of its limits”.

Some of the heavyweight insiders include the first female US secretary of state, Madeleine Albright, 79, who served during Bill Clinton’s second term as US president, Michele Flournoy, 55, a former defence undersecretary who is widely tipped to become America’s first female defence chief if Hillary Clinton is elected, Tim Kaine, 58, Clinton’s vice-presidential nominee and a top Democrat on the Senate Foreign Relations Committee, and Bill Clinton himself, now 70, who has often bragged that as a couple they offer “two for the price of one”.

Others include Strobe Talbott, 70, a deputy secretary of state in Bill Clinton’s first term and now president of the Brookings Institution, Tom Donilon, 61, Obama’s former national security adviser, former CIA director and defence secretary Leon Panetta, 78, former deputy secretary of state Bill Burns, 60, and Middle East expert Wendy Sherman, 67, a former undersecretary of state for political affairs.

Observers say Clinton’s inner circle is packed with long-time personal friends and aides of the Clinton family who have been picked for their loyalty and competence rather than their ideological or party affiliations. In exchange, many senior campaign advisers are tipped for plum postings in a Clinton administration.

According to Foreign Policy magazine, her army of advisers, most of then unpaid, is so big – with as many as “several hundred” writing policy memos for her on a daily basis – that it’s impossible for her to meet them all or to read their policy recommendations and analyses.

There are also about a dozen advisory working groups, consisting of country- or issue-specific subgroups, providing policy support on a wide range of issues from Asia and the Middle East to counterterrorism and cyber security.

Clinton is also closely associated with several think tanks. One of her favourites is the Centre for American Progress, a liberal think tank founded by Podesta and led by Clinton’s long-time ally Neera Tanden, 46, a veteran of both the Clinton and Obama administrations. Podesta, 68, who served as chief of staff to president Bill Clinton and counsellor to Obama, is at the centre of a controversy following WikiLeaks’ release of a trove of more than 50,000 of his hacked emails since last month.

Observers say the Centre for a New American Security (CNAS), a national security think tank jointly founded by Campbell and Flournoy in 2007, is also likely to figure prominently if Clinton becomes president.

CNAS, which has taken special interest in research on Southeast Asia and maritime security in the Asia-Pacific region in the past few months amid rising tension in the South China Sea, has played a more influential role in related policy discussions than some other big-name American think tanks, according to Pang Zhongying, an international affairs expert at Renmin University in Beijing.

Campbell, 59, who was the main architect of the Obama administration’s policy pivot (or rebalance) to Asia and who is enormously popular among America’s Asia-Pacific allies, is believed to be a front-runner for a top job at the State Department if Clinton becomes president.

Former Australian foreign minister Bob Carr said in a 2014 book that Campbell, known as Clinton’s top Asia-Pacific adviser due to his two decades of extensive experience and vast network of contacts in the region, will be secretary of state if Clinton becomes president.

A fluent Japanese speaker and former naval officer, Campbell has a PhD in international relations from Oxford and used to teach at Harvard University.

Before his stint in charge of East Asia and Pacific affairs in Clinton’s State Department between 2009 and 2013, he served as deputy assistant secretary of defence for the Asia-Pacific under Bill Clinton.

In his new book The Pivot: the Future of American Statecraft in Asia, Campbell describes himself as an early supporter of Hillary Clinton and said that during her unsuccessful campaign for the Democrat presidential nomination in 2008 he was “a ‘bitter ender’, staying with her until the very last of a disappointing fight” while many of her other advisers went on to work for Obama, who beat her to become the Democrat nominee.

When Campbell left his State Department post in February 2013, early in the second Obama administration, diplomats in Australia and many other Asia-Pacific nations, with the notable exception of China, lamented that the US had lost its focus on Asia.

Calling him the face of US diplomacy in Asia and Washington’s main strategic thinker about Asia, the Australian newspaper said Campbell “was so effective because of his deep knowledge of Asia, larger-than-life personality, endless energy, diamond-hard mind, sense of strategic realities and closeness to Clinton”.

While he and Clinton earned reputations among China’s Asian neighbours as hard-headed realists who were able to stand up to Beijing’s frequent use of intimidatory tactics, Chinese diplomats and mainland China’s state-controlled media were often incensed by their blunt criticism.

Apart from the pivot policy, Campbell was widely credited with helping to avert a diplomatic crisis in May 2012 when Sino-US relations were roiled by the treatment of dissident Chen Guangcheng, a blind human rights lawyer.

Beijing was initially furious when Chen suddenly turned up at the US embassy in Beijing just days before an official visit to China by secretary of state Clinton. Campbell played a pivotal role in helping to persuade his Chinese counterparts, including then deputy foreign minister Cui, to accept a face-saving deal after long hours of overnight negotiations which effectively granted Chen asylum in the US.

“I don’t want to talk to him any more,” an infuriated Cui reportedly snapped to an aide during one meeting with Campbell.

But despite their frequent, fierce rhetorical clashes, both Cui and Campbell speak highly of each other privately, according to diplomatic sources and US media reports.

“He is very strategic, always comes with a game plan, is never rattled, and if he did express anger, it was as part of a show,” Campbell once said of Cui.

Campbell previously hosted senior Chinese guests at his home when conducting behind-the-scenes diplomacy. In 2010, deputy foreign minister Cui was invited to a “social affair” get-together with a group of State Department officials at Campbell’s weekend retreat in the Virginia countryside, according to The New York Times.

Chinese diplomats and international affairs experts praise Campbell privately as a strategic thinker, a tough and articulate negotiator and a highly respected diplomat.

“His vision, Pentagon background, pro-Japan stance and wide Asia experience makes him stand out among his generation of Asia experts,” Pang said.

Campbell co-chairs with Harvard professor Joseph Nye a group of Asia experts that is part of the Clinton campaign’s advisory team, according to Bloomberg.

David Lampton, a China expert at Johns Hopkins’ school of advanced international studies, said that with advisers like Campbell, Clinton would most likely continue the Asia rebalance policy if elected president.

“I anticipate Ms Clinton will win unless something major, unexpected happens,” he said. “If that’s true, I don’t think she’s likely to reject her signature policy when she was secretary of state and I would understand from the people around her that they’re probably more committed to that policy than they may have been initially.”

Observers also speak highly of a younger generation of advisers who have been playing key roles in Clinton’s campaign.

The campaign’s senior foreign policy adviser, Sullivan, 39, who was Clinton’s deputy chief of staff and director of policy planning when she was secretary of state, and his deputy Rosenberger, 35, who helps communicate with the top advisers outside the campaign team, are the most prominent ones.

Sullivan, a Middle East expert who helped broker the Iran nuclear deal, was once described by former assistant secretary of state Richard Holbrooke as “the one and only person” people must get to know in Clinton’s inner circle.

Clinton has spoken very highly of Sullivan, a Rhodes scholar at Oxford and a visiting professor at Yale Law School, describing him as a “coolheaded, clear-eyed analyst of the problems we faced with our national security”.

Pang said: “Chinese scholars are generally familiar with Campbell and other veteran Asia policy experts, but frankly we still don’t know much about many of the younger advisers around Clinton, who may prove to be a challenge for our decision-makers in the future.”