Vice President Kamala Harris is poised to pick Minnesota Gov. Tim Walz as her vice presidential running mate to help her challenge Donald Trump and JD Vance in November.

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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

Vice President Kamala Harris has officially gotten the vast majority of delegate votes in the virtual roll call that nominates her as the Democratic presidential nominee, the Democratic National Committee said in a statement released late Monday.

The roll call, which concluded on Monday evening, still needs to be certified by Convention Secretary Jason Rae, according to the statement, but the announcement makes Harris's historic nomination effectively official.

-ABC News’ Oren Oppenheim, Brittany Shepherd and Isabella Murray

On a three-hour organizing call with over 100,000 attendees, numerous high-profile progressive democrats came out to support Vice President Kamala's Harris' presidential bid.

Sens. Bernie Sanders and Elizabeth Warren, Reps. Joaquin Castro, Ro Khanna, Ilhan Omar and Jamie Raskin and UAW President Shawn Fain all showed up as well as members of the uncommitted movement who had not yet endorsed Harris but strongly hope she'll win them over in the next few months.

"The energy and the momentum in this election is on our side. And I am so inspired by the organizing in support of Vice President Harris, starting with the win with black women that mobilized a massive zoom call. And now here tonight, we have progressives coming together," Warren said on the call.

Sanders, who has not officially said he endorses Harris -- although he has encouraged voters to go out and support the candidate -- told attendees that "Trump must be defeated" and Harris "must be elected." He noted that it's "imperative that Democrats gain control over the House and the Senate."

"And we in the progressive movement must do all that we can to make that happen," he added.

"I don't know if I can add to what has already been said tonight, but my message is pretty clear, and that is all of us together must do everything that we can to defeat Donald Trump and elect Kamala Harris as our next president," said Sanders.

-ABC News' Gabriella Abdul-Hakim