CHICAGO -- Conceding disappointments during his presidency, yet offering vigorous encouragement for the nation's future, Barack Obama issued an emotional defense Tuesday night of his vision to Americans facing a moment of anxiety and a dramatic change in leadership.

Obama's valedictory speech in his adopted hometown of Chicago was a public meditation on the trials and triumphs, promises kept and promises broken that made up his eight years in the White House.

Arguing his faith in America had been confirmed, Obama said he ends his tenure inspired by America's "boundless capacity" for reinvention, and he declared: "The future should be ours."

His delivery was forceful for most of his speech, but by the end, he was wiping away tears as the crowd embraced him one last time.

Reflecting on the corrosive political campaign, he said, "That potential will be realized only if our democracy works. Only if our politics reflects the decency of our people. Only if all of us, regardless of our party affiliation or particular interest, help restore the sense of common purpose that we so badly need right now."

He made no mention of Republican Donald Trump, who will replace him in 10 days. But when he noted the imminence of that change and the crowd began booing, he responded, "No, no, no, no, no."

One of the nation's great strengths, he said, "is the peaceful transfer of power from one president to the next."

Earlier, as the crowd of thousands chanted, "Four more years," he smiled and said, "I can't do that."

Obama and his family soon will exit the national stage, to be replaced by Trump, a man Obama had argued poses a dire threat to the nation's future. His near-apocalyptic warnings throughout the campaign have cast a shadow over his post-election efforts to reassure Americans anxious about the future.

Indeed, much of what Obama accomplished over the past eight years -- from health-care overhaul and environmental regulations to his nuclear deal with Iran -- could be upended by Trump. So even as Obama seeks to define what his presidency meant for America, his legacy remains in question.

Even as Obama said farewell to the nation -- in a televised speech of just under an hour -- the anxiety felt by many Americans about the future was palpable, and not only in the Chicago convention center where he stood in front of a giant presidential seal. The political world was reeling from new revelations about an unsubstantiated report Russia had compromising personal and financial information about Trump.

Steeped in nostalgia, Obama's return to Chicago was less a triumphant homecoming and more a bittersweet reunion bringing together Obama loyalists and loyal staffers, many of whom long since have left Obama's service, moved to new careers and started families. They came from across the country -- some on Air Force One, others on their own -- to be present for the last major moment of Obama's presidency.

Seeking inspiration, Obama's speechwriters spent weeks poring over Obama's other speeches, including his 2004 keynote at the Democratic National Convention and his 2008 speech after losing the New Hampshire primary to Hillary Clinton. They revisited his 2015 address in Selma, Alabama, that honored America's exceptionalism and acknowledged its painful history on civil rights.

After nearly a decade in the spotlight, Obama soon will become a private citizen, an elder statesman at 55. He plans to take some time off, write a book and immerse himself in a Democratic redistricting campaign.