Kamala Harris, the Democratic Party’s candidate for November’s United States presidential election, has held her first rally with running mate Tim Walz, describing their campaign as a “fight for our future”.

The two took the stage in Pennsylvania to Beyonce’s Freedom just hours after Harris named Walz, the governor of Minnesota, as her vice presidential pick.

Democrats are hoping Walz’s down-to-earth background will win over voters in crucial swing states in the Midwestern region, including Wisconsin and Michigan.

Introducing the Army National Guard veteran and school-teacher-turned-politician, Harris said Walz was “a leader who will help unite our nation and move us forward, a fighter for the middle class, a patriot who believes, as I do, in the extraordinary promise of America.”

A former attorney general of California, 59-year-old Harris has sought to contrast her past as a prosecutor with Republican rival Donald Trump’s criminal record.

She told the crowd of about 10,000 supporters: “This campaign – our campaign – is not just a fight against Donald Trump. Our campaign – this campaign – is a fight for the future.”

Walz, 60, was combative as he went on the attack against 78-year-old Trump.

“He mocks our laws, he sows chaos and division, and that’s to say nothing of his record as president,” Walz said of Trump who was president for four years until 2020. “He froze in the face of the COVID crisis, he drove our economy into the ground, and make no mistake, violent crime was up under Donald Trump,” Walz said.

“That’s not even counting the crimes he committed,” he added to roars of laughter and boisterous applause.

He targeted Republicans for pursuing restrictions on women’s reproductive rights, an issue that has plagued the party since the US Supreme Court in 2022 ended women’s constitutional right to abortion.

“Even if we wouldn’t make the same choice for ourselves, there’s a golden rule: mind your own damn business!” Walz said, drawing a huge ovation.

The first joint appearance by Harris and Walz offered a glimpse of how they might appeal to voters – one a trailblazing Black and South Asian former senator from California, the other a white ex-congressman from the blue-collar US heartland. The Pennsylvania event was the first stop on a multi-day campaign tour through key states crucial to election success: Wisconsin, Michigan, Arizona and Nevada.

Trump and his running mate Senator JD Vance were quick to tag the new competition as too liberal.

“This is the most Radical Left duo in American history,” Trump wrote on his social media platform.

‘Sense of joy’

While most voters will make their choice on November 5 based on the presidential candidate, the choice of a  running mate can help or hurt the ticket as a result of their background, home state popularity and ability to sway important constituencies or independent voters.

A relatively low-profile politician, Walz spent 12 years in the US House of Representatives representing a largely rural district in southern Minnesota. He ran for governor of the state for the first time in 2018 and was returned for a second term four years later. Despite the state not being a traditional Democratic stronghold, Walz won both races with ease.

During his time in office, he has won approval for policies including tuition fee programmes for low-income students, free school meals, goals for tackling climate change, tax cuts for the middle class and expanded paid leave for workers.

Walz, who got the nod ahead of more prominent names including Pennsylvania’s popular Governor Josh Shapiro, on Tuesday spoke of his upbringing in the small town of Butte, Nebraska where he worked on the family farm and where community was a “way of life” with neighbours striving together “for the common good.”

He also lauded Harris’s work and career.

“She took on the predators and the fraudsters, she took down transnational gangs, stood up against powerful corporate interests,” Walz said.

“And she never hesitated to reach across the aisle if it meant improving people’s lives… And she does it all with a sense of joy.”

The vice president’s first joint appearance with her new running mate comes before the Democratic Party convention in Chicago, which starts on August 19.

The noisy rally was a striking reminder of how different the race was before 81-year-old President Joe Biden bowed to mounting concerns over his age and withdrew from the race giving his endorsement to Harris.

Polls show she has erased the lead Trump had built against Biden.

The Harris campaign said it had raised more than $20m after Walz was announced as Harris’s running mate.

Biden described the Harris and Walz ticket as “a powerful voice for working people and America’s great middle class”.