As far as I can tell, different faces, but same old, same old... I mean, literally anyone is better than Biden at the job, considering age...
What do dems worry about her?
Mostly they're afraid that swing voters won't vote for a black woman, but are afraid of saying that out loud.
Not American, so please take this with a grain of salt; but from what I hear she was campaigning in 2020 and dropped out early in favor of Biden because her support in the population was miniscule. So I can imagine they are quite wary whether the perception has changed to the point of her being able to actually win the election.
To be fair, name recognition is hugely important in politics, and in 2020 nobody outside of California had heard of her.
But she has name recognition now that she's been VP. That is a huge bonus.
Some don't consider her progressive enough, some consider her too controversial (eg. non-white, non-male, former prosecutor) to win.
Internal politics is going to be responsible for some of it. This is an unexpected opportunity for individuals to advance their careers or agendas outside of the usual process, and some of them are going to take the opportunity. They might not even dislike the idea of Harris being the nominee, but they want to find a way to use their support to their advantage. The Democrats are hardly a monolith, they're a broad coalition that barely holds together at the best of times, it's not that weird that there would be conflict.
There's also the issue that there hasn't been any sort of democratic process to select a new nominee. Harris makes sense for a number of reasons, and the party does have the authority to nominate whomever they want, but they have to avoid making it look like the party insiders are just coronating a new nominee. It's bad optics, if nothing else. This is also a pretty unprecedented situation, and it seems like no one knew it was going to happen for sure. It makes sense that there's a conversation out in the open about who is going to be the nominee.
As a candidate, she's not the best choice, but she's an improvement over Biden. I doubt she would have won a genuinely competitive primary process. She's probably in the best position to be the nominee at this moment, but there are no doubt plenty of people who feel that this could have been handled better and are going to make their opinions heard.
