Several Black groups have responded to grassroots enthusiasm for Harris with new efforts to mobilize voters to the polls.

Quentin James founded Collective PAC, an organization that supports Black candidates at all levels of government around the country. James helped organize the Monday night Win with Black Men Zoom call -- telling ABC News that the call was just the beginning.

"As someone who's done a lot of fundraising, I've never raised $1.3 million over three or four hours from grassroots donors, I've never seen that kind of momentum," James said. "The energy is inspiring. Each one of those people on the call can organize 10 people or 100 people, and we hope to mobilize all of them."

-ABC News' Tommy Barone and Gabriella Abdul-Hakim

Former President Barack Obama officially endorsed Vice President Kamala Harris on Thursday to be the Democratic Party’s 2024 nominee, saying in a statement that she "has the vision, the character, and the strength that this critical moment demands."

"There is no doubt in our mind that Kamala Harris has exactly what it takes to win this election and deliver for the American people. At a time when the stakes have never been higher, she gives us all reason to hope," he added.

Obama was one of the only high-profile Democrats who had yet to endorse Harris.

-ABC News' Alexandra Hutzler

Former President Donald Trump's campaign is now claiming that it cannot commit to general election debate details until Democrats formally decide on a nominee.

"Given the continued political chaos surrounding Crooked Joe Biden and the Democrat Party, general election debate details cannot be finalized until Democrats formally decide on their nominee," Trump Campaign Communications Director Steven Cheung said in a statement.

Cheung's said Dems "are still holding out for someone 'better.' Therefore, it would be inappropriate to schedule things with Harris because Democrats very well could still change their minds."

Vice President Kamala Harris quickly responded on X, "What happened to 'any time, any place?'"

Trump previously committed to ABC News' debate on Sept. 10, along with invitations from CBS, NBC, and Fox.

This week, he has started to push for a debate hosted by Fox News.

On the campaign trail, Trump has stated that he wants to debate Harris and would be willing to do more than one debate.

-ABC News' Lalee Ibssa, Soo Rin Kim and Kelsey Walsh

Harris spoke with reporters after she landing back at Joint Base Andrews outside Washington Thursday, making a point of saying she is ready to debate Donald Trump on Sept. 10.

"I have agreed to the previously agreed upon September 10 debate. He agreed to that previously. Now it appears he's backpedaling, but I'm ready, and I think the voters deserve to see the split screen that exists in this race on a debate stage, and so I'm ready. Let's go," she said.

The debate is scheduled to be hosted by ABC News, with anchors David Muir and Linsey Davis moderating.

In recent days, Trump has requested another network to moderate the debate.

-ABC News' Justin Gomez