US vice president Kamala Harris has picked Minnesota governor Tim Walz to be her running mate in the presidential election, sources have told the Associated Press.

In choosing Mr Walz, she is turning to 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.

Ms Harris hopes to 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 Republican Donald Trump’s wins in Michigan and Wisconsin in 2016.

Mr 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.

Ms Harris, second gentleman Doug Emhoff and Mr Walz are set to appear together for a rally in Philadelphia on Tuesday evening, recalling a joint 2020 appearance by President Joe Biden and Ms Harris in Wilmington, Delaware.

Mr Walz, 60, is joining Ms Harris during one of the most turbulent periods in modern American politics, promising an unpredictable campaign ahead.

Republicans have rallied around Mr Trump after his attempted assassination in July.

Just weeks later, Mr Biden ended his re-election campaign, forcing Ms Harris to unify Democrats and consider potential running mates during an exceedingly compressed time frame.

The three people spoke on condition of anonymity to avoid pre-empting the official announcement later on Tuesday.

Ms 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, all of whom were white men.

In landing on Mr Walz, she sided with a low-key partner who has proven himself as a champion for Democratic causes.

Mr Walz has been a strong public advocate for Ms Harris in her campaign against Mr Trump and Mr Vance, labelling the Republicans “just weird” in an interview last month.

Democrats have seized on the message and amplified it since then.

During a fundraiser for Ms Harris on Monday in Minneapolis, Mr Walz said: “It wasn’t a slur to call these guys weird. It was an observation.”

Mr Walz, who grew up in the small town of West Point, Nebraska, was a social studies teacher, football coach and union member at Mankato West High School in Minnesota before he got into politics.

He won the first of six terms in Congress in 2006 from a mostly rural southern Minnesota district, and used the office to champion veterans issues.

Mr Walz served 24 years in the Army National Guard, rising to command sergeant major, one of the highest enlisted ranks in the military.

He has often served as a Biden-Harris surrogate, and has made increasingly frequent appearances on national television.

They have included an interview on Fox News that irritated Mr Trump so much that he posted on Truth Social: “They make me fight battles I shouldn’t have to fight.”

Putting Mr Walz on the ticket could help Democrats hold the state’s 10 electoral votes and bolster the party more broadly in the Midwest.

No Republican has won a state-wide race in Minnesota since Tim Pawlenty was re-elected governor in 2006, but GOP candidates for attorney general and state auditor came close in 2022.

Mr Trump finished just 1.5 percentage points behind Democrat Hillary Clinton in the state in 2016.

While Mr Biden carried Minnesota by more than seven points in 2020, Mr Trump has taken to falsely claiming that he won the state last time and can do it again.

Minnesota has produced two vice presidents, Hubert Humphrey and Walter Mondale.