Sanders staying in the race is the best thing Biden could've asked for; he'd be close to double digits down if Warren got the bulk of his support
There's no evidence that she would. Biden is the top second choice of his supporters.
On the other hand, that's been the case throughout Sanders's long, slow slide in support, despite the fact that the vast majority of Sanders's loss in support has (ultimately, in some cases through other candidates) benefited Warren. It continues to be the case that a large portion of Sanders supporters, especially of the Sanders-Biden variety (and also vice versa on the Biden side, especially the Biden-Sanders variety), are not paying much attention and are only minimally aware of the existence of candidates other than Sanders and Biden, the only two candidates with household names before the race. So the professed second choices of Sanders (and Biden) voters in polling should continue to not be taken especially seriously.
