By Eric Bradner, CNN

(CNN) -- Presumptive Democratic nominee Joe Biden and his running mate, California Sen. Kamala Harris, are making their first appearance together Wednesday afternoon for a speech in Delaware.

The speech comes the day after Biden chose Harris after a months-long vice presidential vetting process, making her the first Black woman and first person of Indian descent to be tapped for a major political party's ticket.

Their spouses, Jill Biden and Doug Emhoff, will also attend the speech in Wilmington, Jill Biden spokesperson Michael LaRosa said.

In a tweet that could preview their message, Biden tweeted Wednesday morning that if he and Harris win, "we're going to inherit multiple crises, a nation divided, and a world in disarray. We won't have a minute to waste."

"That's exactly why I picked her: She's ready to lead on day one," he tweeted.

Harris on Wednesday tweeted a biographical video that started with Biden asking her to join the ticket and echoed Biden's core message.

"We are in a battle for the soul of this nation. But together, it's a battle we can win," Harris tweeted.

After the speech, Biden and Harris are set to appear together at an online fundraiser for "grassroots" small-dollar donors.

Whether and how the two can hit the campaign trail, together or separately, remains to be seen. Next week's Democratic National Convention would ordinarily kick off a frenetic two-and-a-half month sprint to the November 3 election, but the coronavirus pandemic has effectively sidelined Biden from campaigning. He spent July delivering weekly speeches detailing planks of his economic agenda.

The last time Biden held a campaign rally -- March 9 in Detroit, on the eve of the Michigan primary -- Harris appeared with him on stage, as the 77-year-old former vice president called himself a "bridge" to a new generation of Democratic leaders.