My friend Chuck Blahous writes on Facebook:

It’s not news to anyone that the D nomination is a two-person race now. But here are some numbers just to amplify the point.
As of this writing, with the vote-counting still continuing in California among other places, 1180 of the convention’s 3979 delegates have been committed. That leaves 2799 still up for grabs. A candidate must have 1991 to win on the first ballot.
Warren would need to receive 69% of the yet-uncommitted delegates in order to win. Her best result so far is 21.2% of the popular vote and a third place finish in the state she represents.
In other words, she needs to more than triple her best outcome in any state, in ALL states (on average) from this point forward. She’s already done, regardless of when she publicly acknowledges it.
Biden and Sanders are still both very much in it, and obviously we have seen huge momentum swings in recent days and could see more in the future. Nevertheless the delegate math is somewhat daunting even for Sanders. He must win 54% of the yet-uncommitted delegates in order to secure the nomination. As of yet, outside of his home state of Vermont, the highest popular vote total he has received in any state is 36.2%.
In order for Biden to win, he needs to basically stay on track. He needs 51% of the remaining uncommitted delegates. Last night he had popular vote percentages in the 40s in several states, and even hit 63.2% in Alabama.