CHICAGO, ILL. -- U.S. Vice presidential nominee Tim Walz and former U.S. president Bill Clinton will headline the Democratic National Convention on Wednesday, the third day of the party's choreographed rollout of a new candidate, Kamala Harris, and her pitch to voters.

In a delicate balancing act, Harris and the parade of Democrats speaking on her behalf all week are looking to harness the exuberance that has swept over their party since President Joe Biden stepped aside while making clear to their supporters that the election will be a fierce fight and frustratingly close.

“So much is on the line in this election,” Harris said Tuesday in Milwaukee, where she spoke at a professional basketball arena in battleground Wisconsin as the convention continued 90 miles away in Chicago. “And understand, this not 2016 or 2020. The stakes are higher.”

And in Chicago hours later, former U.S. president Barack Obama offered his own caution: "Make no mistake, it will be a fight,” Obama said. For all the energy and memes and rallies that have defined the campaign since Harris became the nominee, Obama said, “this will still be a tight race in a closely divided country.”

Harris is working to stitch together a broad coalition in her bid to defeat Republican former U.S. president Donald Trump this fall. She is drawing on stars like Obama and his wife, former first lady Michelle Obama, and other celebrities, officials from the far left to the middle, and even some Republicans to boost her campaign.

And while the theme of Tuesday was “a bold vision for America’s future,” the disparate factions of Harris’ evolving coalition demonstrated, above all, that they are connected by a deep desire to prevent a second Trump presidency.

Convention organizers dubbed the theme for Wednesday “a fight for our freedoms," a nod to the concept around which Harris has organized her campaign. She frames Trump as a threat to abortion rights and personal choices, but also to democracy itself.

Walz's job Wednesday when he accepts the nomination is to introduce himself to Americans who had never heard of the Minnesota governor until Harris plucked him from relative obscurity to join her ticket. His goofy, folksy, Midwestern dad aura has endeared him to Democrats and balanced Harris' coastal background.

In the intense scrutiny that comes with a presidential campaign, Walz has faced repeated questions about embellishing his background. His wife, Gwen Walz, this week clarified that she did not undergo in vitro fertilization but used other fertility treatments after Republicans pointed to multiple times her husband talked publicly about his family's reliance on IVF. JD Vance, the Republican vice presidential candidate, called Tim Walz a liar.

Republicans have also pointed to a 2018 comment in which Walz refers to weapons “that I carried in war” while talking about gun violence. Though he served in the National Guard for 24 years, Walz did not deploy to a war zone.

Clinton, meanwhile, is a veteran of the political convention speech — and famously longwinded. He bored the audience with his keynote address at the 1988 Democratic convention, when he was the young, little-known governor of Arkansas. It damaged his reputation, but he recovered and when he next spoke at a convention four years later it was to accept the Democratic nomination.