Obama praised President Biden and offered support for Harris.
Vice President Kamala Harris officially became the official Democratic presidential nominee during the second night of the Democratic National Convention.
The night included a lively and upbeat roll call vote of delegates that featured a DJ, some celebrities and energetic speeches. Also, Harris, who campaigned in Milwaukee, thanked the crowd in a live-streamed message.
Second gentleman Doug Emoff talked about his long relationship with Harris and touted her vision for the country.
But the night's biggest headline was the return of former President Barack Obama and first lady Michelle Obama to the DNC stage. Both stressed what's at stake in this election and pushed Americans to come together to bring the country to a better future.
The crowd at the United Center was treated to a surprise appearance by Lil Jon when Georgia delegates cast their votes for Kamala Harris.
The rapper sang "Turn Down for What" to a roaring crowd, adding extra lines that repeated the theme: "We're not going back."
At Harris' rally in Milwaukee, the campaign announced in the arena that the vice president will be broadcast into the DNC and that they want the crowd here to "bring the energy."
"I'm really going to need this energy when they broadcast this live, right?" said Jaliah Jefferson, Wisconsin deputy organizing director, Milwaukee. "VP Harris will be beamed into TVs all across the country."
"So when it's our moment, we need to get loud and leave no doubt that Wisconsin is going to send Kamala Harris and Tim Walz to the White House," she added.
Crowds have been waiting for hours to enter the Fiserv Forum -- where the RNC was held last month. The arena is packed with people and it's a party vibe. The music has been pumping loudly, people are dancing and waving their light-up wristbands. The bass in the music is so loud the floor is vibrating.
-ABC News' Selina Wang and Will McDuffie
Kamala Harris' stepson Cole Emhoff paid tribute to his father, second gentleman Doug Emhoff, and how the vice president became part of their blended family, in a video posted on social media ahead of Emoff's DNC speech tonight.
"In 2014, Kamala became Momala," Cole Emhoff said. "She took over Sunday night dinners and taught Doug how to actually cook."
"Our blended family wasn't used to politics or the spotlight, but when Kamala became senator, we were all excited to step up -- especially my dad," Cole Emoff added. "Then, Kamala became vice president. It felt like Doug was a bit out of place on Capitol Hill. I thought: 'What is my goofy dad doing here?'"
-ABC News' Fritz Farrow
The roll call for the DNC has begun.
State delegates will go in alphabetical order, with a DJ playing music related to each state.
