Clinton joined Obama on stage after his speech, and the President and his 2008 primary rival clung together in a shared moment of symbolism: the nation's first African-American leader entrusting its future to the woman who could become its first female commander-in-chief.
Obama was in Philadelphia at the Democratic National Convention 12 years to the day after he shook politics with a convention speech in Boston that encouraged Americans to look at the common threads that unite them. He offered a similarly empowering vision of the nation Wednesday, saying America doesn't need a "self declared savior" like Donald Trump to fix it.
Undaunted by the experience of a presidency that unfolded in a time of crisis and deep ideological divides, he renewed his faith in the idea of a unified nation. The speech crystalized the two visions of America emerging this election season, following last week's Republican National Convention in which Trump blasted Obama for leaving the country divided and plagued by crime.
"The America I know is full of courage, and optimism, and ingenuity," Obama said. "The America I know is decent and generous. Sure, we have real anxieties -- about paying the bills, protecting our kids, caring for a sick parent. We get frustrated with political gridlock, worry about racial divisions; are shocked and saddened by the madness of Orlando or Nice."
He went on: "But as I've traveled this country, through all fifty states; as I've rejoiced with you and mourned with you, what I've also seen, more than anything, is what is right with America."
Obama then made an impassioned case for Clinton, saying no man or woman had ever been as prepared to be president.
"Nothing truly prepares you for the demands of the Oval Office," Obama said. "But Hillary's been in the room; she's been part of those decisions."
He acknowledged Clinton had made mistakes, but compared her to Teddy Roosevelt's valiant striver who errs, but also knows great triumphs.
"Hillary Clinton is that woman in the arena," Obama said.
He also made an appeal to Bernie Sanders supporters who are still cool on Clinton.
"You've got to get in the arena with her, because democracy isn't a spectator sport," he said.
Throughout the night, speaker after speaker leveled heated criticism of Trump aimed at undermining his image as a tough guy who understands Americans. Vice President Joe Biden painted Trump as completely unqualified for the presidency.
"He is trying to tell us he cares about the middle class. Give me a break. That's a bunch of malarky," Biden said. "This guy doesn't have a clue about the Middle Class. Not a clue."
The crowd roared with approval, chanting "not a clue."
Biden said Trump was unable to handle the complexities of a dangerous world.
"No major party nominee in the history of this nation has ever known less or has been less prepared to deal with our national security," he said.
Biden used his address on the third night of the Democratic National Convention to appeal to middle-class voters, a group Clinton is under pressure to win over. Leveraging his blue-collar bona fides, he argued Clinton is intimately familiar with the economic disenfranchisement that helped power Trump's rise.
On Thursday, Trump told a crowd at a rally in Davenport, Iowa, the Democrats are acting "like everything is wonderful."
"I watched last night, and it was like all beautiful roses," he said.
'Hillary gets it'
"Everybody knows she is smart," Biden said. "Everybody knows she is tough. But I know what she is passionate about. I know Hillary. Hillary understands. Hillary gets it."
Former New York Mayor Michael Bloomberg, meanwhile, said he was not a Democrat or a Republican but appeared at the convention to demolish his fellow billionaire's reputation in business.
"I believe we need a president who is a problem-solver, not a bomb-thrower," said Bloomberg.
He quipped that unlike Trump, he didn't start his business empire with a "million dollar check from my father."
"Trump has left behind a well-documented record of bankruptcies, thousands of lawsuits, angry shareholders and contractors who feel cheated, and disillusioned customers who feel ripped off," Bloomberg said. "Trump says he wants to run the nation like he's run his business. God help us!"
"I am a New Yorker, and I know a con when I see one."
He went on: "The bottom line is: Trump is a risky, reckless, and radical choice. And we can't afford to make that choice!"
The night of the DNC also offered a big opportunity for Tim Kaine, Clinton's vice presidential pick, who introduced himself to an audience unfamiliar with his years as a governor and senator in Virginia.
He affected an impression of Trump and used the billionaire's verbal tick "Believe Me" to ridicule him as a "slick talking, empty promising, self promoting, one man wrecking crew."
Noting that his son, Nat, deployed with the US Marines this week, Kaine quickly slammed Trump for raising the possibility that his administration wouldn't always defend NATO allies.
Kaine said his son would "protect and defend the very NATO allies that Donald Trump now says he wants to abandon."
He made a case that Americans should trust Clinton.
"I trust Hillary Clinton with our son's life," Kaine said. "You know who I don't trust? Donald Trump."
"You cannot believe one word that comes out of Donald Trump's mouth. Not one word," Kaine said, slamming the GOP nominee as a "slick talking, empty promising, self promoting, one man wrecking crew."
The night's underlying theme was security — national security, economic security and safety from gun crime.
Leon Panetta, the former CIA director and secretary of defense, lashed out at Trump over his apparent call on Russian intelligence agencies to help find emails that Hillary Clinton deleted from her private server.
"Today, Donald Trump today once again took Russia's side. He asked the Russians to interfere in American politics. Think about that for a moment. Donald Trump, who wants to be president of the United States, is asking one of our adversaries to engage in hacking or intelligence efforts against the United States of America to affect an election," Panetta said.
"As someone who was responsible for protecting our nation from cyberattacks, it's inconceivable to me that any presidential candidate would be that irresponsible," he said. "Donald Trump cannot become our commander-in-chief."
During his remarks, some Bernie Sanders supporters began to chant "No More War!" but were drowned out by counter chants of "USA, USA."
Soon after Panetta spoke, the Trump campaign released a statement criticizing the former defense secretary's stance.
"It is alarming that Leon Panetta would, through his silence, excuse Hillary Clinton's enablement of foreign espionage with her illegal email scheme and her corrupt decision to then destroy those emails and dissemble her 'private' server to hide her crimes from the public and authorities," Trump senior policy adviser Stephen Miller said. He also argued that it was Clinton who is endangering national security with her policies in the Middle East and North Africa.
The FBI recommended not to bring criminal charges against Clinton earlier this month related to her private email server.
But the night will likely be most remembered for the power of Obama's rhetoric.
He appeared deeply emotional as he began to take his leave of the nation he has led.
"For all the tough lessons I've had to learn; for all the places I've fallen short; I've told Hillary, and I'll tell you what's picked me back up, every single time," Obama said. "It's been you. The American people."