Joe Biden and Lindsey O. Graham were hurtling over the Hindu Kush mountains, bound for Kabul and a war that both men knew was veering badly off track.

Biden was two weeks away from being sworn in as vice president and had chosen Graham, who he said had the “best instincts in the Senate,” to accompany him on the trip. Graham, eager to carve out a new role in a changing Washington, jumped at the invitation.

Both men wanted to send a message to then-Afghan President Hamid Karzai — and to their fellow Americans — that the 2008 election was behind them, and that Republicans and Democrats were now united in their resolve to arrest the long-neglected Afghanistan war’s decline.

“The campaign is over,” Graham said, “but the war is not.”

Nearly 11 years, two presidential elections and a historic presidential impeachment hearing have passed since Biden and the Republican senator from South Carolina flew off together to Kabul. Today their friendship, their war zone trip and its bitter aftermath offers a view into how two of the most prominent politicians of their era have tried to adapt to a changing Washington, a norm-breaking presidency and the country’s rancorous politics. The pressures have tested their ideals, their friendship and, at times, their faith in their country.

As impeachment shifts to the Senate, the two men seem to be on a collision course.

Graham’s attacks threaten not only their friendship but also the very rationale of Biden’s Democratic presidential campaign, one that promises to return the country to a less partisan time — an era when Biden could work with Republicans as partners and friends. It’s a vision that even some in his own party dismiss as naive. If Biden can’t break through with Graham, critics wondered, what chance does he have with other Republicans?

Last month, in an attempt to shift attention away from President Trump’s alleged misdeeds in Ukraine, Graham asked the State Department for materials related to Hunter Biden’s work for a Ukrainian energy company. He also demanded the declassification of transcripts of calls between the elder Biden and Ukrainian officials.

Only a few weeks earlier, Graham said he had no intention of investigating the Bidens. “I’m not going to turn the Senate into a circus,” he vowed.

Then, under pressure from the White House, Graham insisted that his relationship with Biden shouldn’t preclude a proper Senate investigation.

The line of inquiry infuriated Biden. “Lindsey is about to go down in a way that I think he’s going to regret his whole life,” the former vice president said, shaking his head.

A few days later, Biden’s frustration spilled out in an exchange with an 83-year-old Iowa farmer who suggested that Biden and his son had acted improperly in Ukraine. “You’re a damn liar!” said Biden, striding toward the man, who held his ground. “That’s not true. No one has ever said that.”

It was, in fact, similar to what Graham had suggested.

In January 2009, such rancor between the two men seemed inconceivable. As Biden and Graham huddled on their plane, the senators pored over CIA reports that showed al-Qaeda was reestablishing training camps in Pakistan’s tribal areas, just outside the reach of U.S. forces. In Afghanistan, the U.S. military and CIA reports spoke to staggering levels of government corruption, mounting Afghan casualties and a resurgent Taliban that was rapidly advancing toward the capital.

Their military plane approached Kabul International Airport, ringed by snow-covered mountains. Down on the tarmac, a clutch of generals and Foreign Service officers waited in the cold. Soon their traveling party would board a Blackhawk helicopter that would whisk them to the presidential palace, where Karzai was waiting.

They agreed that they were going to push the Afghan leader to crack down on longtime political allies and family members who had been looting the country, according to contemporaneous interviews done for Bob Woodward’s 2010 book, “Obama’s Wars.” Neither had much faith that their pressure on Karzai would work.

“I dread this meeting,” Graham said.

“Me, too,” Biden replied.

Power of the Senate to heal

Five days after their joint meeting with Karzai, Biden and Graham were back in Washington, where Biden took to the Senate floor to bid farewell to the place that shaped his view of the nation and its politics.

There were no female senators when Biden was elected. No computers. No fax machines. By the time he was leaving, there had been 1,900 senators in American history, and Biden had served with 320 of them. “The United States Senate has been my life, and that is not a hyperbole,” he said. “It literally has been my life.”

His speech that day focused on the power of the Senate — and friendships like the one he was building with Graham — to alter the course of American politics and heal the wounds of slavery and segregation.

Biden recalled his bonds in the Senate with three former segregationists: Robert C. Byrd (D-W.Va.), Jesse Helms (R-N.C.) and Strom Thurmond (R-S.C.). From his deathbed, Thurmond asked Biden to speak at his funeral. To many Democrats, Thurmond was an unrepentant racist. To Biden he was a man saved by his service in the Senate.

“Every good thing I have seen happen here, every bold step taken in the 36 years I have been here, came not from the application of pressure by interest groups, but through the maturation of personal relationships,” Biden said.

It was Thurmond’s retirement at age 100 that opened a pathway for Graham’s ascendance to the Senate. In the years that followed, Graham and Biden crisscrossed the globe together with their mutual friend Sen. John McCain (R-Ariz.).

When the Iraq War looked lost in 2005, Biden and Graham traveled to Baghdad, returning home to warn President George W. Bush that the country was on the brink of civil war. Their 2009 trip to Afghanistan had been just as eventful. Over dinner, Biden and Graham hammered Karzai on his failings, the country’s growing heroin trade and his brother’s alleged corruption.

“We can’t come to Afghanistan without hearing about your brother,” Graham told Karzai. When the Afghan president accused the Americans of indifference to civilian deaths, Biden abruptly ended their meal. “This is beneath you, Mr. President,” Biden said. He and Graham stormed out together. Back in Washington, President-elect Barack Obama told reporters that he was drafting Graham as “one of our counselors in dealing with foreign policy.”

This was the kind of politics — collegial, bipartisan, conciliatory — that Biden wanted to celebrate. As he bid goodbye to the Senate, Biden recalled his relationship with one more reformed segregationist, former Democratic senator John Stennis of Mississippi.

In 1988, Stennis had given Biden a prized conference table from his office where he and his fellow Dixiecrats had gathered to plot the demise of the civil rights movement. Stennis had dubbed it “the flagship of the Confederacy.”

“It’s time this table passes from the man who was against civil rights into the hands of a man who was for civil rights,” Biden recalled Stennis telling him. By that point in his life, cancer had ravaged Stennis’s body and cost him a leg. From his wheelchair, Stennis told Biden of his late-in-life conversion and belief that the civil rights movement had done “more to free the white man than the black man.”

“It freed my soul,” Stennis said. “It freed my soul.”

To some, the table would have been a symbol of hatred, a reminder of the men who fought to perpetuate America’s original sin and the racism that still infected the nation’s politics. To Biden, it represented possibility and the transformative powers of the Senate.

Shaped by different eras

In a dark conference room at the National Guard Memorial Museum, Graham stood to Biden’s right, dressed in his crisp Air Force uniform. It was late June 2015. After 33 years as a lawyer in the reserves, he was retiring. Biden, just two weeks removed from his son Beau’s funeral, had come to help send him off.

A few days later, Graham was touring Iowa as part of his long-shot presidential run. In the back seat of a rental car, he grew emotional as he spoke about Biden. “If you can’t admire Joe Biden as a person, then you’ve got a problem,” he told HuffPost. “You need to do some self-evaluation, because what’s not to like?

“He’s the nicest person I think I’ve ever met in politics,” he continued. “He is as good a man as God ever created.”

Graham’s comments in the back of the rental car came just days after Trump glided down the golden escalator at Trump Tower, launching his presidential campaign with an unprecedented attack on Mexicans and McCain’s heroism in Vietnam.

Graham responded by calling Trump a “jackass” who was “appealing to the dark side of American politics” and had no place in the Republican Party. “He’s a race-baiting, xenophobic, religious bigot,” Graham added later in the year. “I’d rather lose without Donald Trump than try to win with him.”

Graham voted for Evan McMullin, a long-shot independent, in 2016. By 2017, though, he was already acceding to the demands of Trump’s Washington. Graham dined with Trump at the White House and gave the president his new cellphone number. Trump had broadcast his old one from a campaign stage in a fit of pique. He became a regular Trump golf partner and, in what was becoming the most direct path to power and influence in the Trump White House, a cable news defender of the president.

Though they were friends, Graham and Biden had been shaped by different eras. Biden entered a Senate dominated by World War II veterans and the apocalyptic demands of the Cold War. Graham came to Washington in 1995, when American power was at its apex and lawmakers could spend months focused on President Bill Clinton’s infidelities with a White House intern. He was the floor manager during the Clinton impeachment hearings, where he tried and failed to persuade the Senate to call Monica Lewinsky to provide live testimony.

Before his death in 2018, McCain had asked both men to eulogize him. Their speeches captured their contrasting views of America and its politics.

Biden recalled a moment during the Clinton years when party leaders chastised him and McCain for sitting next to each other in the Senate chambers. “This is the mid-’90s,” Biden said. “It began to go downhill from there.”

But at an even stormier moment in American politics, Biden’s eulogy was unapologetically optimistic. “Many of you travel and see how the rest of the world looks at us. They look at us a little naive, so fair, so decent,” Biden said. “We’re the naive Americans. That’s who we are. That’s who John was.”

Graham also praised McCain’s courage and capacity for forgiveness in the wake of his captivity in Vietnam and his presidential defeats. But in eulogizing his old friend, Graham focused on his own and his country’s limits. Unlike McCain, Graham wasn’t a war hero or political maverick who could buck the president or his party on hot-button issues such as health care, immigration and climate change.

“The void to be filled by John’s passing is more than I can do,” Graham said on the floor of the Senate as he fought back tears. “Don’t look to me to replace this man.”

Inevitable confrontation

So far Biden has built his presidential campaign around many of the same “soul of America” sentiments that surfaced in his McCain eulogy. Graham, meanwhile, has moved ever closer to a full embrace of Trump, the president who McCain pointedly banned from attending his funeral.

Until recently, Graham and Biden had been able to avoid a direct confrontation. But Biden’s presidential aspirations and the increasingly contentious impeachment battle have made a confrontation inevitable.

Trump has put Biden at the center of his impeachment defense, insisting that Biden used his influence over U.S. foreign policy to engineer the firing of a Ukrainian prosecutor who was investigating Burisma, a Ukrainian gas company that employed Hunter Biden. There’s no evidence that Biden acted to protect his son or that Hunter was ever a target of the probe. Even as he has described Biden as “a fine man,” Graham has defended Trump’s efforts to dig up dirt on his rival and suggested that Biden and his son might be guilty of wrongdoing.

The Senate Judiciary Committee, chaired by Graham, has no clear oversight role regarding Ukraine, but Graham has asked for transcripts of Biden’s calls with Ukraine’s former president and records of Hunter Biden’s interactions with State Department officials. “I hope there’s nothing there. Reveal the transcripts. Trump released the transcripts,” Graham said in an interview with Fox News Radio last month. “All I’m asking is that somebody look at this line of inquiry. It does look very suspicious to me.”

Biden responded by trying to shame Graham. Asked by CNN if he had any words for his friend, Biden paused for several seconds to think, and replied: “Lindsey, I . . . I . . . I’m just embarrassed by what you’re doing, for you. I mean, my Lord.”

The two men have spent part of the past two weeks pondering the state of their relationship and what it says about the nation’s increasingly bitter politics. “My friendship with Joe Biden, if it can’t withstand me doing my job, it’s not the friendship I thought we had,” Graham said. “Everything I said about him in 2015 is true. I admire him as a person. I think he’s always trying to do right by the country. . . . But we’re not going to allow a system in America where only one side gets looked at.”

As Biden’s campaign bus rolled through Iowa recently, reporters asked what was driving Graham to investigate him and his son. Biden offered a simple explanation: “Donald Trump. Donald Trump. Donald Trump.”

Paul Kane and Julie Tate contributed to this report.