WASHINGTON — At the Warner Theater in downtown Washington the other night, former Vice President Joe Biden kicked off a new tour at which he discussed his new book, “Promise Me, Dad: A Year of Hope, Hardship and Purpose.”

The orchestra and balcony were jam-packed with his supporters and friends, and they absorbed and applauded his heartfelt remarks as he recounted what the year 2015 was, as he and the Biden family supported and endured the major brain cancer battle of his elder son, Beau, that finally claimed his life.

The title was drawn from the promise his devoted son drew from his father near the end: “You’ve got to promise me, Dad, that no matter what happens, you’re going to be all right. … Give me your word as a Biden.”

It was a formulation that Joe Biden had for years used in his home state of Delaware where his word was his bond with his constituents. President Obama, in his subsequent obituary at Beau’s funeral in Wilmington, used it when he described himself as a member of the Biden family sharing its grief.

Joe Biden writes in the book that he affirmed his promise to Beau, in which his son clearly urged that he remain committed to his lifelong service in public life. Beau also shared in it as Delaware’s attorney general and prospective governor, which he almost certainly would have become in an approaching election.

It so happened that his father was weighing a third presidential bid in 2016 upon completion of his second vice-presidential term. Joe candidly told the Warner Theater crowd on this night that a few days after Beau’s funeral, he reported back to work at the White House and resumed his duties at home and abroad.

The former vice president reveals in the book that he had a small core group of advisers headed by old political aides Mike Donilon and Steve Ricchetti draft a 2,500-word announcement speech preaching “We’re one America, bound together in this one great experiment of equality and opportunity and democracy. And everyone — and I mean everyone — is in on the deal.” It went on: “And most of all, we had to speak to those who felt left behind. They had to know we got their despair.”

Biden also acknowledges in the book that key liberal Democrats, including former presidential candidates Bill Bradley and Gary Hart, urged him to run. But at a final campaign meeting held on Oct. 20, 2015, Donilon suddenly told him: “I don’t think you should do this.”

Donilon was, Biden writes, “speaking as a friend. … The pain he read on my face was off the charts. Mike also knew that Jill would have supported the decision to go, but he thought he thought saw dread in her eyes.” So he told Jill, children Hunter and Ashley, President Obama, Donilon and Ricchetti that he was not going to run in 2016, and he stuck to it.

But afterward, with the shocking defeat of Hillary Clinton and the startling elevation of Donald Trump to the Oval Office, the situation had suddenly dramatically changed. Biden continued to say he had no regrets at what he still believed not running was in the best interest of himself and his family at the time. When voices in the audience at the Warner the other night began to chant “Run, Joe, Run” and the like, he obviously was warmed by the reaction. By this time he had already said on several television talk shows that while he still was not planning to run in 2020, adding that “I’m not closing the door” either.

He also has made a point of acknowledging his age of 74 would be a legitimate cause of voter concern. He has said that if he runs, he would fully disclose his medical records, having had two brain aneurysms nearly two decades ago.

Meanwhile, the “American Promise” book tour is scheduled in more than a dozen states in the next several weeks, with Biden relating this intensely emotional personal experience, along no doubt with more audience inquiries about his next political intentions.

Jules Witcover’s latest book is “The American Vice Presidency: From Irrelevance to Power,” published by Smithsonian Books. You can respond to this column at juleswitcover@comcast.net.