Washington(CNN) It was February 2008 when a snowstorm suddenly overwhelmed the flight path of two American helicopters, forcing them to make an unexpected landing on a mountaintop in Afghanistan.
On board the aircrafts overlooking Taliban territory were Joe Biden and Antony Blinken, his then-top adviser on the Senate Foreign Relations Committee, along with a few other members of the committee, according to two sources on the trip.
When the helicopters landed, soldiers accompanying them established a perimeter around the narrow mountain peak while they decided what to do next. Blinken hopped out of his helicopter to check on Biden.
The source on the trip told CNN that they "remember Tony being unbelievably calm throughout the entire thing and occasionally quite funny. He did not blame anyone for what had happened."
"Tony just knew how to keep everything under control. He mirrors Biden in that way. They are both calm under pressure," they said.
Blinken, the newly confirmed secretary of state, has worked with Biden for almost 20 years, and many describe him as having the closest personal relationship with the President of anybody in the Cabinet. They forged that bond in the field, on a tremendous number of foreign trips they took together when Biden was the chairman of the Senate Foreign Relations Committee, but also through a US presidential campaign, the shared experience of personal loss and ties between their families.
Over the years, Biden has relied on Blinken to deal with crisis scenarios in an even-keeled manner, to morph his foreign policy ideas into reality, to support his political endeavors, and to be a loyal friend.
"Tony has been a part of Joe's evolution, learning, and changes as he has confronted challenge after challenge over decades," said Delaware Democratic Sen. Chris Coons, who sits on the foreign relations committee and called Blinken "an irreplaceable part of Joe Biden's inner core team."
Blinken is expected to be privy to every major decision Biden makes as President, according to multiple sources who spoke with CNN. That deep level of involvement will be driven by Biden administration's belief that foreign policy is intrinsically tied to domestic policy and the need to strengthen democracy at home, but it is also a reflection of their sturdy comfortable relationship, the sources explained.
"They will continue to nurture their relationship, and it will be wide ranging," said an official who is planning to join Blinken's State Department. "They will see each other a lot. And some of it may be over casual dinners at the White House."
When Blinken began working with Biden on the Senate Foreign Relations Committee in 2002, the Iraq War debate was ongoing, accelerating their relationship, which may have otherwise matured at a slower pace.
"The war drums were beating," said a source who was working on the committee at the time. "The relationship forged pretty quickly."
Blinken worked alongside Biden when he voted in favor the Iraq War -- a vote that has been repeatedly scrutinized, and one that Biden and Blinken have both said Biden regretted.
After that initial bonding experience over the most fundamental foreign policy question of war and peace, Blinken was involved in almost every foreign policy declaration or policy that Biden put forth during his time in the Senate and as vice president.
Even when Biden went against the grain -- for example, in advocating for a smaller troop presence in Afghanistan when other national security officials advocated for a troop surge in the early days of the Obama administration -- Blinken advocated for his views at the interagency level and fine-tuned the policy Biden was driving it forth.
"Blinken channels Biden's passion and energy into a constructive outcome," said the source on the Afghanistan trip.
"It was Biden's style to absorb information and give feedback extemporaneously, in the moment, which does not lead to a crisp foreign policy paper," said the source who worked on the Senate Foreign Relations Committee with them. "But Blinken is skilled in communications and writing. He could do it."
Blinken's tight-knit relationship with Biden is what career diplomats and those close to Blinken's inner circle expect to fuel his efficacy as America's top diplomat.
"The challenge always with the secretary of state and the president is does the secretary of state really speak for the president? And when he says something, does the foreign government that he's talking to believe that that is what the president actually thinks?," former career US diplomat Lew Lukens told CNN. "When Tony Blinken travels the world, people will know what he says is what Joe Biden believes and thinks. He speaks for the President, and that is incredibly important for a secretary of state. And we didn't always have that."
Blinken has not solely been a foreign policy adviser to Biden, he has also been intimately involved in aspects of Biden's political career.
In 2008, the night Biden got home from being announced in Springfield as Barack Obama's running mate, he had a couple staffers up from Washington to his home to plan. Blinken was one of just four, explained a source who worked with them on the campaign. After that, he went on the road with Biden as he traveled the country campaigning.
"Truthfully, almost all of the messaging and speeches day in and day out were about domestic issues, not foreign policy. But Sen. Biden wanted Tony there by his side because he knew the presidency was always shaped by foreign policy decisions, and he wanted uninterrupted time with Tony to plan. But he also wanted something else: a friend and trusted confidante," said the source who worked with them on the 2008 campaign. "As many of us on the plane were falling asleep, you could usually see a light on up in the front two seats, and it was Sen. Biden and Tony talking late into the night."
And there is another layer that deepens the connection: Blinken's wife, Evan Ryan, was Biden's deputy campaign manager when he ran for the nomination in 2008. After working on the Biden transition, Ryan is now serving in the Biden White House as the executive secretary.
The two couples have been loyal friends throughout times of hardship when they have experienced family loss, according to sources familiar with their relationship. Biden's father died in September of 2002 when he first met Blinken, and then in 2015, Blinken's stepfather and Biden's son, Beau Biden, both passed away.
"President Biden is personally close to both Tony Blinken and Evan Ryan and Tony has been an incredibly loyal, capable and effective adviser, staffer and personal friend of the sort that is rare in Washington," said Coons.