Biden pulls proportionally from all the Democratic candidates. About 59 percent of Biden voters say Clinton is their second choice — about the same overall level of support Clinton earns among the Democratic electorate. And about 12 percent of Biden backers would go to Sen. Bernie Sanders, a smaller percentage than Sanders’s overall level of support.
Of course, this math could change if Biden enters the race. He might be able to win the backing of Democratic bigwigs who are unwilling to support Sanders but would be open to an alternative to Clinton. And with Biden in the race, Clinton’s (along with the other candidates’) numbers would drop.
But Biden does not have an obvious camp of support right now.