Tom Brokaw is senior correspondent for NBC News.

For almost half a century, Joe Biden has been a conspicuous presence in the nation's capital, a gregarious old-school Democrat with friends on both sides of the political divide. He ran twice for his party's nomination as president and lost by wide margins, but he didn't get on the train back to Delaware. He returned to the life of a public servant. When Barack Obama, the newcomer, looked for ballast on his presidential ticket, Biden was a wise and effective choice.

How ironic that the bookends of Biden's happy-warrior political career are the deaths of his first wife and 1-year-old daughter in a car accident just before he reached Washington, and then 42 years later, the death of his son Beau, who was stricken with brain cancer. Beau, an Iraq veteran, had planned to run for governor of Delaware after serving two terms as the state's attorney general, and he was the odds-on favorite. A young man of such promise, many could see the Oval Office in his future.

"Promise Me, Dad" is Joe Biden's poignant, instructive and deeply affecting account of a family's struggle against a vicious brain cancer, played out against the demands of his job as vice president and the temptations of another run for the presidency. It is also a touching account of the cruel realities of cancer, especially cancer that strikes your child.

As I have learned from my own cancer battles, when one member of a family develops the disease, all members are affected. "Promise Me, Dad" takes you deep into the Biden family's approach to sharing roles and emotions when cancer attacks.

Beau Biden's diagnosis of glioblastoma came after a mysterious siege of muscle and verbal struggles. He tried to shake off the early symptoms by using a favorite expression: "All good. All good." In fact, it was all bad. When neurologists in Philadelphia raised the possibility of glioblastoma, the deadly brain tumor that killed Ted Kennedy, the family doctor was brutally candid when asked where the Bidens should go for treatment. He blurted out, "If it's The Monster, it doesn't matter where we go."


It was The Monster.

The Bidens chose MD Anderson, the Houston temple of cancer treatment staffed with world-renowned surgeons. (In our current political climate, it is not lost on the reader that Beau's primary physicians were both immigrants — one from the Middle East, the other from China.) They began an aggressive yet delicate treatment that involved cutting away the tumor without doing damage to Beau's motor or verbal skills.

The first stage went well, so the vice president left Houston to return to his White House duties and to build a stealth movement for a Biden for President campaign for 2016. His team from earlier campaigns was up and running, and the early signs looked promising, even against the presumption that Hillary Clinton would be the Democratic nominee.

One who did not like the prospect of Biden running for the Democratic nomination was his boss, and friend, President Obama. At lunch after lunch Obama expressed his opposition in clear but subtle terms. It was obvious to Biden that Obama had concluded Clinton was almost certain to be the nominee. As Biden puts it, "A number of the President's former staffers, and even a few current ones, were putting a finger on the scale for Clinton."

The vice president understood the president's concerns. How could Biden do his job as vice president, run for his party's nomination and be there for Beau? What kind of chaos would that mean for the final 18 months of the Obama presidency?

They were a team, Obama and Biden, and like so many successful teams they represented a yin and yang. Biden acknowledges that "there were times when we were unhappy with each other," but they kept their differences off the nightly news. The vice president confesses he thought there were occasions when his boss was deliberate to a fault. When Biden saw a distant, troubled look in the president's expression, he would counsel: "The country can never be more hopeful than its president. Don't make me 'Hope.' You gotta go out there and be 'Hope.' " For his part, the president confided to aides that he wanted Joe's advice, just in 10-minute, not 60-minute, increments.

As the vice president resumed a role he relished, as the administration's point man on vexing international issues, he spent time on the phone with the president of Iraq, flew to Central America to deal with the issue of children from the region pouring across the U.S. border and traveled to Moscow for his first meeting with Vladmir Putin.

Biden and Putin had a contentious discussion about the placement of an American missile defense shield close to the Russian border. The vice president couldn't convince the steely Putin that the system was there to protect against Iranian missiles. Remembering that President George W. Bush, in his first meeting with Putin, said he looked into his eyes and got a "sense of his soul," Biden recalls that he looked directly at Putin and said, "Mr. Prime Minister . . . I don't think you have a soul." Biden writes: "He looked at me for a second and smiled back. 'We understand each other.' "

Back home, hopes for Beau's recovery were fading fast, and he was readmitted to MD Anderson, where his team of specialists was preparing a radical approach. Oncologists today use a variety of techniques to unleash the body's immune system on cancer cells, and it shows signs of being a historic breakthrough. But it is complex and traumatic. The patient gets a megadose of antibodies, followed by surgery to cut away the excessive parts of the tumor. Then comes the go-for-broke step: A live virus designed to replicate itself is injected into the tumor and effectively goes to war on the cancer cells.

That war between the live virus, Beau's immune system and the cancer cells would be hard on him, the doctors warned. And so it was. He went home to tough it out, but it was a losing game. He developed a paralysis on one side of his body, a fluid buildup in his brain and pneumonia. His effervescent personality disappeared into a haze.

Transferred to Walter Reed National Military Medical Center in Washington, Beau briefly seemed to be making a recovery, but it was a false note. With his extended family, Secret Service agents, physicians and Walter Reed attendants gathered in a solemn huddle in and around his room, Beau's body finally succumbed to the cancer.

The vice president recorded in his diary: "May 30, 7:51 p.m. It happened. My God, my boy. My beautiful boy."

Beau's send-off in Delaware was a tribute to his life as attorney general and an Iraq veteran. Much was said of what would have been his future life of service and honor.

His father's political team continued preparing for a Biden for President campaign, more encouraged every day by what they saw as ever-brighter prospects. Biden was driven onward by his love of political campaigning, his confidence that he could prevail, the pace of promising developments and calls from friends such as former New Jersey senator Bill Bradley: "Joe, sometimes the man meets the moment. Tragedy has bonded you to the public, and you can build on that. Joe, this is your moment."

But Biden's longtime friend and political guru Mike Donilon saw something else: Biden's continuing pain from the loss of Beau, and he said quietly, "I don't think you should do this." It was a moment when friendship overwhelmed politics, a rarity in the high-octane environment of a presidential campaign.

The next day, Biden, with Obama at his side, formally announced that he would not be a candidate. He was at peace with his decision.

As a cancer patient, I am deeply gratified that Biden wants to stay actively involved in the "moonshot," a monumental undertaking to develop a massive, coordinated effort to accelerate the many breakthrough developments in cancer treatment. His new role is an extension of a conversation he had with Beau in the early stages of his son's illness. When the gravity of his situation was becoming clear, Beau called his dad to his side and said: "You've got to promise me, Dad, that no matter what happens, you're going to be all right. Give me your word, Dad. You're going to be all right."

A promise kept.

Promise Me, Dad
A Year of Hope, Hardship, and Purpose

By Joe Biden

Flatiron. 260 pp. $27