Harris already has secured a majority of the delegates. Clearly the Dem party coalesced around Harris within 24 hours, which indicates the pump was primed in all likelihood. The funds that were bottled up flowed almost immediately along with public support. It's hard to imagine a truly open DNC given today - Harris just has to solidify a VP pick soon.
They seemed to start right off to try flipping the age issue around on Trump but despite his various gaffs and so on, there's no chance it sticks - he's got better Teflon than Reagan did.
I did see an image going around already which made me chuckle, of a $5K donation to Harris from Trump in 2011 for her AG campaign. (Which she apparently didn't keep.)