Former US president Barack Obama and his wife Michelle have called on the nation to embrace Kamala Harris in speeches at the Democratic National Convention.

Mr Obama wrapped up the second night of the convention in Chicago, praising the Vice President and her running mate Governor Tim Walz while taking aim at Republican rival Donald Trump.

The former president called Mr Trump “a 78-year-old billionaire who hasn’t stopped whining about his problems since he rode down his golden escalator nine years ago”.

“It’s been a constant stream of gripes and grievances that’s actually gotten worse now that he’s afraid of losing to Kamala,” the former president said.

“We don’t need four more years of bluster and chaos. We’ve seen that movie – and we all know that the sequel’s usually worse.”

For all the energy and memes and rallies of the campaign, he said, “this will still be a tight race in a closely divided country.”

“Make no mistake, it will be a fight,” he said.

“For all the incredible energy we’ve been able to generate over the last few weeks, this will still be a tight race in a closely divided country — a country where too many Americans are still struggling and don’t believe government can help.”

He praised President Joe Biden and his decision to withdraw his candidacy for a second term.

“History will remember Joe Biden as a president who defended democracy at a moment of great danger,” Mr Obama said as the crowd chanted, “Thank you, Joe.”

“I am proud to call him my president, but even prouder to call him my friend.”

Former first lady Michelle Obama told the convention “something wonderfully magical is in the air”.

“It’s the contagious power of hope,” she said. “America, hope is making a comeback.”

She tore into Mr Trump, who has long attacked the first black president and first lady, before harkening back to a recent comment the Republican nominee made about preserving so-called “black jobs.”

“His limited and narrow view of the world made him feel threatened by the existence of two hard-working, highly educated, successful people who also happened to be black,” he said.

“Who’s going to tell him that the job he’s seeking might be one of those ‘black jobs’?”

She warned that Mr Trump’s policies and rhetoric “only makes us small. And let me tell you … going small is never the answer”.

“Going small is petty… it’s unhealthy… and, quite frankly, it’s unpresidential,” she said, calling Ms Harris and Mr Walz “good, big-hearted people”.

In an appearance perhaps intended to needle Mr Trump, his former press secretary Stephanie Grisham — now a harsh critic of her former boss — also took to the convention stage earlier in the evening.

She said Mr Trump “has no empathy, no morals and no fidelity to the truth”.

“I love my country more than my party,” she said. “Kamala Harris tells the truth. She respects the American people. And she has my vote.”

Senators Chuck Schumer, the Senate Democratic leader, and Bernie Sanders, the Vermont independent beloved by progressives, praised Ms Harris.

“I look forward to working with Kamala and Tim to pass this agenda,” Mr Sanders said. “And let’s be clear. This is not a radical agenda.”

Second gentleman Doug Emhoff, who would become the nation’s first gentleman if his wife wins the presidency, shared personal details about their relationship with Ms Harris — their cooking habits, their first date and her laugh, which is often mocked by Republican critics.

“You know that laugh. I love that laugh,” Mr Emhoff said as the crowd cheered. “Her empathy is her strength.”

Among the celebrities appearing at the convention on Tuesday night were director Spike Lee and actors Sean Astin, Eva Longoria and Wendell Pierce.