Bennett is out of the question since he's running re election, Harris too even if she wasn't running for Senate she's only a statewide AG, Booker's not ready and no wife so gay rumors will persist.
Of course, some of the "diversity" choices like Harris will end up on the short list solely for public consumption rather than because they're seriously being considered.
It would be kind of odd, though, for Harris to even participate in the vetting if she's in the middle of a Senate campaign.
The difference is that Harris would not have been elected Senator yet.
But I don't think that matters in Calfornia, where Harris would be the major frontrunner. A Republican opponent would be the underdog, and a Democratic opponent in a runoff would have a tough time bashing the presidential ticket.
The biggest question is whether the Attorney General of California is qualified to run for national office. I think they can make that argument, but it's easier with a Senator, Governor, top Cabinet official, or a member of the congressional leadership (IE- Xavier Becerra.)
Both Biden and Ryan had safe re election bids where there was no threat of them even losing while Bennet is in a purple state where there will be a competitive race. When was the last time a VP had to run a competitive race in their own state while also being on a national ticket.
