Joe Biden’s presidential campaign has gotten a couple shots in the arm over the past 24 hours, thanks to the exits of Pete Buttigieg and now Amy Klobuchar from the presidential field. Each had a base of more moderate-ish supporters that could logically shift toward Biden, and they’ve bowed out while there’s still enough time for Biden to take advantage.

That sound you hear is Bernie Sanders supporters pleading for Elizabeth Warren to follow suit.

Warren, like Buttigieg and Klobuchar, looks to be a long shot to actually win the Democratic nomination; she hasn’t finished higher than third place in any state, and she may not win any state on Super Tuesday, either. Indeed, she looks like she might even lose her home state of Massachusetts to Sanders.

But Warren doesn’t appear to be going anywhere, and that’s an increasingly big problem for Sanders. That’s because her exit would probably be an even bigger boon to Sanders than the others will be for Biden.

As The Washington Post’s Philip Bump reported in late January, the most pronounced second-choice shift in the Democratic primary field was Warren supporters going to Sanders. A Quinnipiac University poll at the time showed 35 percent of Warren supporters said Sanders was their second choice. In early February, that stood at 33 percent.

By contrast, that January poll showed 22 percent of Klobuchar supporters said Biden was their second choice. Their most popular second choice? Buttigieg. So if Biden wants to clean up with Klobuchar supporters, he might have to rely upon being their third choice.

The path from “Buttigieg supporter” to “Biden supporter” is also a bit muddled and uncertain. Quinnipiac’s February poll tested Buttigieg backers’ second choices, and they were:

  1. Klobuchar: 26 percent
  2. Warren: 26 percent
  3. Biden: 19 percent
  4. Sanders: 11 percent
  5. Mike Bloomberg: 9 percent

Buttigieg’s support also seemed to occupy something of a middle ground between the liberal and more-moderate sides of the party. He did well among almost all demographics when he won Iowa, for example. So while the logical migration to Biden seems apparent for more-moderate Klobuchar backers, it’s perhaps not quite so obvious when it comes to Buttigieg’s supporters. And given Buttigieg had significantly more support in national polls (about 10 percent on average vs. about 5 percent for Klobuchar), that will be a big question.

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.

There’s even a shot they could put her over the top in Massachusetts, where polls between her and Sanders are close, and Buttigieg and Klobuchar were combining for about 20 percent. And if they put her over the top there, it wouldn’t just rob Sanders of a win; it might give her reason to stick around longer. Warren is still racking up endorsements, after all, including from the National Organization for Women’s PAC and Emily’s List on Monday.

Perhaps that’s why Sanders reserved one of his latest rallies before Super Tuesday for Warren’s home state, on Saturday. But he arguably needs a knockout blow there even more than he did at the time of the rally.