The joint appearance provided a striking reminder of how the pandemic has upended the usual rhythms of a presidential campaign. Four years ago, Hillary Clinton and her newly selected running mate, Senator Tim Kaine of Virginia, made their debut appearance in front of thousands of people inside an arena in Miami. Mr. Biden, on the other hand, barely strayed from his Wilmington home for his appearance with Ms. Harris.
Though scores of onlookers gathered outside Alexis I. du Pont High School to see what they could, the event was closed to the public, depriving it of the typical soundtrack of big campaign speeches. There was no burst of applause, for instance, at the long-awaited moment when Mr. Biden introduced Ms. Harris as “your next vice president of the United States.”
Still, those realities didn’t interfere with online fund-raising.
On Facebook, the Biden campaign sought to keep up the flow of donations on Wednesday, running hundreds of ads prodding supporters to kick in small contributions.
The Facebook ads included some broad talking points, saying that Ms. Harris “is a leader in holding the Trump administration accountable” and that “Joe and Kamala are ready to fight for hard-working Americans who have been hurt by Trump and the G.O.P.’s divisive politics.”
The Trump team was nearly immediate in its digital response, flooding its multimillion-dollar Facebook campaign with ads calling Ms. Harris a far-left liberal and painting the Biden-Harris ticket as “two of our Nation’s most RADICAL Democrats.”
“It’s REAL Americans vs. SOCIALISTS,” another ad read.
The Trump campaign also turned the Harris announcement into a fund-raising opportunity online, asking for small-dollar donations that it claimed would help air a 30-second, ready-for-TV ad that attacked Ms. Harris as a member of the “radical left” and “a phony.”
In his own speech, Mr. Biden directly addressed Mr. Trump’s early attacks on Ms. Harris, quoting some of the adjectives he had used, like “nasty” and “mean.”