Obama, speaking as voting was underway in the critical battleground state Pennsylvania, even refashioned his old campaign rallying cry, "Yes, We Can," to "Yes, She Can," which beamed on a screen over the crowd.

Obama said that the last few years, starting with the pandemic, have been hard for Americans, with high prices and other impacts putting a squeeze on working families.

"I get why people are looking to shake things up. I mean, I am the hopey-changey guy. So I understand people feeling frustrated and we can do better," Obama said.

But he painted Trump as out-of-touch and not the choice to lead the country to change, calling him a "bumbling" billionaire "who has not stopped whining about his problems since he rode down the golden escalator" in 2015 to launch his first campaign.

The former president's appearance at the University of Pittsburgh was his first appearance at a campaign rally for Harris as he sets off on a swing-state tour on her behalf. Obama last month appeared at a Harris fundraiser in California and in August spoke at the Democratic National Convention in August,

Obama, eight years out of power, has been one of the Democratic Party's most reliable surrogates to galvanize voters. Until he was elected president in 2020, Joe Biden had also taken on that role for Democrats, but this year, since ending his reelection campaign and letting Harris ascend to the ticket, he's yet to hit the trail.

As the nation's first Black president, Biden's appearance for Harris underscores the history-making nature of her own political career. Harris, the first woman, Black person or person of South Asian descent to serve as vice president, would be the first woman to serve as president if elected next month.

Glenda Ellison, a 71-year-old retired schoolteacher and Democrat from Pittsburgh, said she is feeling "a little nervous" about the election but "prayerful that it's going to turn out in our favor."

Ellison said she sees Obama as a party spokesperson with a large following who can hopefully sway voters that might be on the fence about voting for Harris.

"As a former president, and also as a Black president, I think that is something that might connect with the African American community, the fact that we do have our Black president supporting another Black candidate," said Ellison, who is Black.

Obama was among the key Democrats who were part of a behind-the-scenes effort to encourage Biden, his former vice president, to drop out of the 2024 race.

Obama and Harris have been friends for two decades since he ran for Senate in Illinois. She campaigned for him when he sought the presidency in 2008.

Pennsylvania is a state Obama won in his 2008 and 2012 presidential races, but Trump won in 2016. Biden narrowly carried it in 2020 and the state is shaping up to be one of the most closely contested in this year's race.

Trump was in the eastern part of the state Wednesday for back-to-back rallies in Scranton and Reading. He also campaigned in eastern Pennsylvania over the weekend when he returned to Butler, where he was shot in July as he survived an assassination attempt.

Obama's appearance was also aimed to bolster the reelection campaign of Pennsylvania Sen. Bob Casey, who is being challenged by Trump-endorsed Republican David McCormick.

Earlier in the day, Obama visited a campaign office in Pittsburgh, where he brought pastries for volunteers and thanked them for their work, according to his office.

"I'm excited because that's what Allegheny County needs, is him to promote Harris and Walz, just really to get the momentum going and to get those blue votes out," Sherry Werner, a 60-year-old who works at the University of Pittsburgh Medical Center.

Werner, who was wearing a Harris button pinned to her sweater, said she is volunteering to help the campaign and feels more momentum already than in past years, and noted the long line of people waiting to get into the event hours before Obama was set to take the stage.

"Who doesn't love Obama?" she said.