It has been less than two weeks since President Biden dropped his re-election bid and threw his support behind Vice President Kamala Harris.

Already, Ms. Harris has closed the gap with former President Donald J. Trump in some national polls. The Harris campaign said it had raised more than $200 million in a week. Ms. Harris’s supporters even broke attendance records on Zoom, with one group gathering more than 160,000 people on a single call.

After more than a year of a presidential contest that was defined by its stability — and people who said they really didn’t like their options — there has been a clear vibe shift.

With just under 100 days left until Election Day, we wanted to check in on this brand-new race. We spoke to Zoom rally organizers, first-time campaign donors and people who were previously planning to sit the whole thing out.

Where did the new energy come from, and how sustainable is it?

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