PHILADELPHIA — Kamala Harris introduced Minnesota Gov. Tim Walz to the nation as “the vice president America deserves” at a raucous rally Tuesday in Philadelphia aimed at building momentum for the newly minted Democratic presidential ticket in the sprint toward Election Day.

“I set out to find a partner who can help build this brighter future,” Harris said, joking that the past two weeks since she stepped into the race have been “something of a whirlwind.”

“I’m here today because I’ve found such a leader.”

Walz soaked up the adulation of Harris and then turned it right around as he took the microphone, declaring to the vice president: “Thank you for bringing back the joy.”

From there, he laid out his biography and took on their Republican opponents, former President Donald Trump and Ohio Sen. JD Vance, for their “backward agenda.”

Revving up the crowd for the rigorous campaign to come, Walz told the roaring crowd, “We’ve got 91 days. My God, that’s easy. We’ll sleep when we’re dead.”

In choosing the 60-year-old Walz, Harris is elevating a Midwestern governor, military veteran and union supporter who helped enact an ambitious Democratic agenda for his state, including sweeping protections for abortion rights and generous aid to families.

It was her biggest decision yet as the Democratic nominee and she went with a broadly palatable choice — someone who says politics should have more joy and who deflects dark and foreboding rhetoric from Republicans with a lighter touch, a strategy that the campaign has been increasingly turning to since Harris took over the top spot.

“He’s the kind of person who makes people feel like they belong and then inspires them to dream big … that’s the kind of vice president America deserves,” Harris said.

Walz is joining Harris on the ticket during one of the most turbulent periods in modern American politics. Republicans have rallied around former President Donald Trump after he was targeted in an attempted assassination in July. Just days later, President Joe Biden ended his reelection campaign, forcing Harris to scramble to unify Democrats and decide on a running mate over a breakneck two-week stretch.

Harris hopes Walz will help her shore up her campaign’s standing across the upper Midwest, a critical region in presidential politics that often serves as a buffer for Democrats seeking the White House. The party remains haunted by Trump’s wins in Michigan and Wisconsin in 2016. Trump lost those states in 2020 but has zeroed in on them as he aims to return to the presidency this year and is expanding his focus to Minnesota.

Since Walz was announced, the team raised more than $10 million from grassroots donations, the campaign said.

Walz is far from a household name; an ABC News/Ipsos survey conducted before he was selected but after vetting began showed that nearly 9 in 10 U.S. adults did not know enough to have an opinion about him. Harris devoted much of her speech to telling the audience about Walz life and work.

“To those who know him best, Tim is more than a governor,” she said.

Harris, the first Black woman and person of South Asian descent to lead a major party ticket, initially considered nearly a dozen candidates before zeroing in on a handful of serious contenders.

Trump has focused much of his campaign on appealing to men, emphasizing a need for strength in national leadership and even featuring the wrestler Hulk Hogan on the final night of the Republican National Convention. Harris’ finalists — all white men — marked an acknowledgement of the Democrat’s need to at least try to win over some of that demographic.

She personally interviewed three finalists: Pennsylvania Gov. Josh Shapiro, Arizona Sen. Mark Kelly and Walz. Harris wanted someone with executive experience who could be a governing partner, and Walz also offered appeal to the widest swath of the diverse coalition.