The Democratic National Convention that began Monday in Chicago holds particularly high stakes for the party one month after an unprecedented mid-campaign switch from Biden to Harris. The opening night was designed as a handoff from the incumbent to his hand-picked successor -- albeit four years before he intended for her to follow him.

Harris made an unannounced appearance onstage as the convention's prime-time program began Monday evening to thank Biden for his leadership in advance of his speech later on.

"Joe, thank you for your historic leadership, for your lifetime of service to our nation, and for all you'll continue to do," she said. "We are forever grateful to you."

Democrats are looking to the weeklong event to slingshot Harris toward a faceoff with Republican Donald Trump, whose comeback bid for the White House is viewed by Democrats as an existential threat. Having taken over the ticket just one month ago, Harris must now win over a divided country that is viewing her more positively but still making up its mind about the election.

Not even a month ago, Democrats were deeply divided over foreign policy, political strategy and Biden himself, who was holding on after a disastrous debate by claiming he had a better chance than any other Democrat -- including Harris -- of beating Trump.

Part of introducing Harris and running mate Tim Walz will be first giving a graceful exit to the incumbent president, who is slated to deliver the main address Monday.

The Democratic Party would almost certainly have been in a far worse state if Biden had continued to cling to the nomination. He faced growing concerns about his mental and physical acuity after struggling to complete sentences during his debate against Trump.

After deciding to step aside and endorse Harris, Biden will instead receive a hero's welcome in his final turn in the spotlight 52 years after being elected to the Senate from Delaware.

Democrats took turns praising Biden's leadership and his choice in Harris to succeed him. They tried to connect both Biden and Harris to what the party sees as the governing pair's most popular accomplishments: leading the country out of the depths of the COVID-19 pandemic, pushing for massive investments in the country's infrastructure, working to lower healthcare costs and promoting clean energy.

"Thanks to Joe and Kamala, we reduced the price of prescription drugs, repaired roads and bridges and replaced lead pipes," said South Carolina Rep. Jim Clyburn, whose 2020 endorsement was critical to Biden winning that primary. He added that one of Biden's best decisions was "selecting Kamala Harris as his vice president and endorsing her to succeed him."

Former Secretary of State Hillary Clinton, who was greeted with prolonged applause, saluted Harris while noting her potential to break the "highest, hardest glass ceiling" to become America's first female president. Clinton was the Democratic nominee in 2016, but she lost that election to Trump.

"Together, we've put a lot of cracks in the highest, hardest glass ceiling," Clinton said, invoking a metaphor she referenced in her concession speech eight years ago. "On the other side of that glass ceiling is Kamala Harris taking the oath of office as our 47th president of the United States. When a barrier falls for one of us, it clears the way for all of us."

Clinton also saluted Biden for stepping aside, saying, "Now we are writing a new chapter in America's story."

Highlighting the party's generational reach, Clinton, 76, followed New York Rep. Alexandria Ocasio-Cortez, 34, who endorsed Harris while delivering the first mention of the war in Gaza from the convention stage, addressing an issue that has split the party's base ever since Hamas' Oct. 7 attack and Israel's resulting offensive.

Outside the arena, thousands of protesters descended on Chicago to decry the Biden-Harris administration's support for the Israeli war effort.

Harris "is working tirelessly to secure a cease-fire in Gaza and bringing the hostages home," Ocasio-Cortez said, drawing cheers from the crowd.

Meanwhile, Democrats also looked to keep the focus on Trump, whose criminal convictions they mocked and who they asserted was only fighting for himself, rather than "for the people" -- the night's official theme.

Michigan State Sen. Mallory McMorrow hoisted an oversized copy of "Project 2025" -- a blueprint for a second Trump term that was put together by the Heritage Foundation, a conservative think tank -- onto the lectern and quoted from portions of it.

"So we read it," McMorrow said. "Whatever you think it might be. It is so much worse."

Trump, the former president, has publicly disavowed any interests in the policies outlined in Project 2025, but he has close ties to its authors and campaign aides had praised its work in the past.

Democrats kept abortion access front and center for voters, betting that the issue will propel them to success as it has in other key races since the Supreme Court overturned Roe v. Wade two years ago. Speakers Monday included three women whose healthcare suffered as a result of that decision. And the convention program included a video of Trump praising his own role in getting Roe struck down.

A month after a major union leader spoke at the Republican convention, Democrats on Monday featured several labor leaders to appeal to a core party constituency. United Auto Workers President Shawn Fain led the crowd in chanting that "Trump is a scab" as he credited Biden and Harris with standing by striking autoworkers last year.

The convention program also honored the civil rights movement, with an appearance from the Rev. Jesse Jackson, the founder of the Chicago-based Rainbow PUSH Coalition, who is ailing with Parkinson's disease. There were several references to Fannie Lou Hamer, the late civil rights activist who gave a landmark speech at a Democratic convention in 1964.

Hamer was a former sharecropper and a leader of the Mississippi Freedom Democratic Party, a racially integrated group that challenged the seating of an all-white Mississippi delegation at the 1964 Democratic National Convention. Hamer spoke on Aug. 22, 1964 -- exactly 60 years before Harris is set to accept the Democratic nomination and become the first Black woman and first person of South Asian descent to be the presidential nominee of a major party.

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Associated Press writers Will Weissert and Josh Boak in Chicago, Ali Swenson and Michelle L. Price in New York and Chris Megerian in Washington contributed to this report.