Obama has been a vocal supporter of Harris since she ascended to the top of the Democratic ticket after President Joe Biden stepped aside in July following a poor debate performance against Trump, the Republican former president.
Obama, whose White House term ended in 2017, is still popular with his party's base. The rally he headlined at the University of Pittsburgh, held while Harris campaigned in Nevada and Arizona, is the first of several events he plans to do in battleground states in the coming weeks.
.— Barack Obama (@BarackObama) @KamalaHarris doesn't have "concepts of a plan" for the American people – she has actual plans to make your life better. And she's more than ready to be President. Let's help her get elected: https://t.co/P9hoDajB1P pic.twitter.com/Yf0onbSvhQOctober 11, 2024
"I get it why people are looking to shake things up," Obama said to a crowd of supporters on Thursday.
"I understand people feeling frustrated, feeling 'We can do better.' What I cannot understand is why anybody would think that Donald Trump will shake things up in a way that's good for you, Pennsylvania."
Obama, who argued Trump only cared about his own ego and money, stressed that Harris was raised in the middle class and believes in American values.
"Kamala is as prepared for the job as any nominee for president has ever been."
Obama is not the only former president the Harris campaign intends to deploy on the campaign trail.
Bill Clinton, like Obama a two-term Democratic president, and a former Arkansas governor, will make stops in Georgia on Sunday and Monday before travelling to North Carolina for a bus tour later in the week in an effort to reach rural voters.
Youth are among a critical part of the coalition that the Harris campaign hopes will propel her to victory. But voter registration among young people in 34 states is down compared with four years ago, according to data updated in September from the Center for Information & Research on Civic Learning and Engagement at Tufts University.
US Vice President Kamala Harris speaks during a campaign event in Chandler, Arizona. (AP PHOTO)
The number of people between the ages of 18 and 29 registered to vote in Pennsylvania in September was 15 per cent lower than it was on Election Day in 2020, the centre's data showed.
Obama and his wife, Michelle, gave rousing speeches in support of Harris at the Democratic National Convention in August; the former first lady is expected to campaign further for Harris as well.
Harris and Trump remain in a close race, and winning Pennsylvania could be key to winning the White House in a battle that will ultimately be determined by the Electoral College.