Live updates: Harris and Walz take the stage in 1st joint campaign rally

Donald Trump reacted to the news that Vice President Kamala Harris is poised to pick Minnesota Gov. Tim Walz as her running mate.

Trump, in a campaign email, claimed Walz "would be the worst VP in history" and said the governor was "even worse" than Harris.

Read the full statement here:

"It's no surprise that San Francisco Liberal Kamala Harris wants West Coast wannabe Tim Walz as her running-mate - Walz has spent his governorship trying to reshape Minnesota in the image of the Golden State. While Walz pretends to support Americans in the Heartland, when the cameras are off, he believes that rural America is 'mostly cows and rocks'. From proposing his own carbon-free agenda, to suggesting stricter emission standards for gas-powered cars, and embracing policies to allow convicted felons to vote, Walz is obsessed with spreading California's dangerously liberal agenda far and wide. If Walz won't tell voters the truth, we will: just like Kamala Harris, Tim Walz is a dangerously liberal extremist, and the Harris-Walz California dream is every American's nightmare."

Vice President Kamala Harris is poised to pick Minn. Gov. Tim Walz as her vice presidential running mate. Who is the two-term governor joining her on the ticket?

Read more: Who is Tim Walz? Harris poised to pick Minn. governor as VP running mate

Minn. Gov. Tim Walz has been a strong public advocate for Harris in her campaign against Trump and Vance, labeling the Republicans "just weird" in an interview last month.

Kamala Harris is poised to pick Minnesota Gov. Tim Walz to be her VP running mate, ABC confirms.

As of this moment, no calls have been made to any candidates.

Vice President Kamala Harris' presidential campaign is touting its robust ground game in Pennsylvania, saying it's taking "nothing for granted" in the state, ahead of her running mate reveal, which is expected on Tuesday.

About 33,000 people signed up to volunteer for the campaign in Pennsylvania in the last 15 days, according to a campaign memo. The campaign boasts nearly 300 staffers across three dozen offices in the state, the memo said.

The campaign also said it was "doing the work to make inroads in historically-safe Republican areas."

The campaign sought to contrast Harris' record with former President Donald Trump's, citing the vice president's time as a prosecutor and saying she "is committed to keeping our communities safe and locking up dangerous crooks, criminals, and predators."

"With only three months until Election Day, Trump's campaign still lags far behind in the infrastructure needed to win with just three offices in Pennsylvania," the Harris campaign memo said. "He's shown he doesn't want these voters."

-ABC News' Will McDuffie, Fritz Farrow and Gabriella Abdul-Hakim