Barack Obama headlines DNC as ex-Republicans endorse Harris

Former US president Barack Obama has returned to the national stage to boost his longtime Democratic ally Kamala Harris in her 11th-hour presidential bid against Republican Donald Trump.

America's first Black president, Obama has thrown his considerable political capital behind Harris as she seeks to make history herself on November 5 as the first woman and first Black and South Asian person to be elected US president.

Obama was preceded by his wife Michelle, who tops Democrats' wish list as a future president.

"I don’t know about you, but I’m feeling fired up! I am feeling ready to go," Obama told delegates to the convention in Chicago, echoing his first presidential campaign slogan.

"We have a chance to elect someone who has spent her entire life trying to give people the same chances America gave her."

But he warned November 2024 contest "will be a tight race in a closely divided country."

Earlier, US Jewish Senator Bernie Sanders during his speech called to "end this horrific war in Gaza, bring home the hostages and demand an immediate ceasefire".

Republicans who have left the fold since Trump's takeover of their party crossed the aisle on Tuesday night to address the convention, including Trump's former White House press secretary Stephanie Grisham and former Trump voter Kyle Sweetser.

Grisham described her journey from a Trump "true believer" to the first senior White House staffer to resign after the January 6, 2021, attack by Trump supporters on the US Capitol.

Conservative voters who dislike Trump have been one of the Democrats' hoped-for prizes. The challenge will be persuading them to get to the ballot box in November and vote for Harris, versus staying home or writing in a presidential candidate.

Obama impact

Harris' fledgling campaign, still light on policy specifics, has coasted on the enthusiasm of Democrats relieved by the departure of 81-year-old president, Joe Biden.

Obama outlined what he believes will lift Harris to victory while also warning Democrats about the tough task they face over the next 11 weeks. The former first lady emphasised the need for the country to turn the page on fear and division.

Trump and his vice presidential running mate, JD Vance, are barnstorming battleground states this week in a bid to steer attention away from the convention in Chicago and highlight Trump's policy differences with Harris.

At a campaign stop in Howell, Michigan, Trump repeated claims that Harris took a permissive approach to law enforcement.

"You can't walk across the street to get a loaf of bread. You get shot, you get mugged, you get raped," he said.

Harris and her vice presidential pick, Minnesota Governor Tim Walz, traveled to Milwaukee on Tuesday for a campaign rally in the same venue as last month's Republican National Convention, where Trump formally received his party's nod.

At 63, Obama looms large in moments of crisis, including during the messy deliberations that led Biden to step out of the race last month and endorse his vice president.

Along with former House Speaker Nancy Pelosi, he is viewed by some as having been a driving force behind the party revolt.

Biden took centre stage on Monday, the assembly's opening night, drawing an extended standing ovation from the party faithful and delivering a speech that stretched well past midnight.

Like his successors, Obama presided over a closely divided country during his two terms from 2007-2017. But his healthy electoral margins in 2008 and 2012 are now considered out of reach for Harris.