Kamala Harris and her running mate Minnesota Governor Tim Walz will appear together at a rally in Philadelphia, hoping to enhance her bid to become the next U.S. president.

Walz had been on a vice-presidential shortlist with a string of other Democratic figures seen as broadening Harris's appeal as she sprints into the contest against Donald Trump.

Aiming to make history as the first woman U.S. president, Harris – already a trailblazer as the first female and first Black and South Asian vice president – has little time before Election Day on Nov. 5.

"I am proud to announce that I've asked Tim Walz to be my running mate," she posted on X.

"As a governor, a coach, a teacher, and a veteran, he's delivered for working families like his. It's great to have him on the team."

President Joe Biden quickly expressed support for his deputy's "great decision" to choose Walz, saying the duo "will be a powerful voice for working people and America's great middle class."

Expectations had always been that Harris would pick a white man to balance the ticket and help win over working-class, white, male voters, a demographic that propelled Trump to victory in 2016.

Walz fits that description as a 60-year-old Midwesterner with a folksy manner, decades of military experience and a rural perspective.

He dismisses the "nonsense" of Trump and Republican running mate J.D. Vance, and he is also a gun-owner who tweets about hunting, goes ice-fishing and rides rollercoasters with his daughter.

The onetime teacher and school sports coach flipped a Republican district in 2006 to win a seat in the House of Representatives in a state seen as light years from the coastal elites of California, Harris's home turf, or the East Coast.

At the same time, Walz will appeal to the left for championing cannabis legalization, worker protections, abortion rights, and tighter firearm restrictions.

'Heartland' Democrat

Trump's campaign branded the Minnesotan as a "dangerously liberal extremist" seeking to impose California values on the nation.

Democratic grandee Nancy Pelosi swatted such criticism aside, telling MSNBC that Walz "is right down the middle. He's a heartland of America Democrat."

Walz earned enthusiastic endorsements from Democratic liberals as well as centrists like Senator Joe Manchin, who called him "the real deal."

After being named by Harris, he said it was the "honor of a lifetime" and quipped it felt like "the first day of school."

The pair will hit the campaign trail immediately, launching a five-day swing through battleground states starting Tuesday in the biggest prize, Pennsylvania.

It has been a remarkable journey for Harris, who only entered the race last month when 81-year-old Biden withdrew, bowing to mounting concerns over his age.

The former prosecutor and senator has since obliterated fundraising records, attracted huge crowds and dominated social media on her way to erasing what had been Trump's growing lead in polls over Biden.

The latest University of Massachusetts Amherst poll has Harris leading Trump nationally by three percentage points, 46 to 43, compared to a four-point lead for Trump over Biden in January.

In the swing states that decide U.S. elections, Harris is neck and neck with Trump, who shocked the world with his 2016 victory but was beaten by Biden in 2020.

Campaign test

Picking a running mate was seen as the first big test for Harris.

Now, she and Walz will face the first hurdle of their ground game as they head from Pennsylvania to Wisconsin, Michigan, Arizona and Nevada.

Pennsylvania is part of the "blue wall" that carried Biden to victory in 2020 -- one reason many had expected Harris to pick state governor, Josh Shapiro.

Vance, speaking to supporters Tuesday in Philadelphia, said her refusal to pick Shapiro, who is Jewish, as her running mate showed she "listened to the Hamas wing of the party."

Harris-Walz campaign co-chair Mitch Landrieu shot back, telling CNN that Harris "reiterates our support for Israel" and that Walz "has done the same."

Trump was riding high last month after surviving an assassination attempt at a rally, and then using the Republican convention to highlight his image of vigor against the physically frail Biden.

But with Biden's exit and Harris's fast start, he is scrambling to recalibrate.

At a rally Saturday, Trump called Harris a "Marxist" who would cause an "economic crash."