Bernie Sanders’s Elizabeth Warren problem

That’s also a key point with Warren. Not only is the second-choice path for her voters more explicitly pointed at Sanders than between Klobuchar and Biden or Buttigieg and Biden, but there are more of them who could migrate. Warren averages about 15 percent in national polls — about the combined total of Buttigieg and Klobuchar. So it’s a bigger block, and it would probably be a bigger windfall for Sanders.

That bigger base of support, of course, is part of the reason Warren is staying in this race. She looks as though she could win delegates on Super Tuesday and — ideally for her — perhaps outperform former New York mayor Mike Bloomberg and make this a three-candidate race. Buttigieg’s exit could potentially help her, judging by those second-choice polls. Warren has long been an attractive second choice for voters of many different stripes. Perhaps she’s as intrigued by the prospect of a shrunken field as is Biden.

And in that way, the early exits of Buttigieg and Klobuchar could be doubly bad for Sanders. Their supporters are going somewhere, but that somewhere doesn’t seem at all likely to be Sanders, who was the second choice of just 11 percent of Buttigieg backers and 9 percent of Klobuchar backers in the Quinnipiac polls. If they go to Biden, he could compete with Sanders for a delegate lead. If they go to Warren, she may see fit to stay in the race and keep splitting up the liberal vote.