On the eve of the fourth Democratic primary debate, the top tier of presidential candidates is arguably down to two or three. We’ve already seen a handful of candidates rise and fall this year, and with 16 weeks left until the Iowa caucus, there is still plenty of time for that to happen again before a single vote is actually cast.

So let’s once again look at polls that ask Democratic voters who their second choice for president is, as this helps us understand who stands to benefit if one of the candidates falters in the polls. For example, if you read my piece on voters’ second choices shortly after the first debate in June, you could have predicted that Sen. Kamala Harris’s subsequent decline in the polls would be good news for former Vice President Joe Biden and Sen. Elizabeth Warren, as there was a fair amount of overlap in their supporters.

And since the third Democratic debate about a month ago, I’ve seen four national Democratic primary polls that asked respondents for their backup candidates. Interestingly, the polls’ numbers didn’t always agree. Still, there are a few takeaways I think are common to all four.

But first — the polls. Immediately after the September debate (specifically, Sept. 13-16), Civiqs conducted a poll that found that Warren was the first choice for 30 percent of respondents, Biden was first choice for 24 percent, Sen. Bernie Sanders for 14 percent, South Bend, Indiana, Mayor Pete Buttigieg for 7 percent and Harris for 6 percent. And as for second-place picks, there was a close race for second place among Warren supporters — Sanders, Buttigieg and Harris were all popular picks. But among a plurality of Biden supporters (37 percent), Warren was the clear second choice. Additionally, over half of Sanders supporters went with Warren as their second choice; Rep. Tulsi Gabbard (11 percent) was the only other second-choice candidate who registered in the double digits with them. As for supporters of other candidates, their sample sizes were too small (fewer than 100 respondents) to be useful.

Over the same date range, NBC and The Wall Street Journal conducted a poll that found that Biden was the first choice of 31 percent of Democrats, Warren 25 percent, Sanders 14 percent, Buttigieg 7 percent and Harris 5 percent. But while Warren was still the top second choice of Biden supporters, not as many (27 percent instead of 37 percent) picked her as No. 2 in this poll. Sanders (16 percent of Biden supporters) and Buttigieg (15 percent) weren’t far behind either. As for Warren supporters, their most popular second choice was Sanders at 29 percent, with Biden (18 percent), Harris (16 percent) and Buttigieg (15 percent) also getting respectable shares.

In addition, Morning Consult asks voters for their second choices as part of its weekly tracking poll, the most recent of which was conducted Sept. 30 to Oct. 6. When asked who their first choice for president was, 33 percent of respondents said Biden, 21 percent said Warren, 19 percent said Sanders, 6 percent said Harris and 5 percent said Buttigieg. And although Warren was still the top second choice of Biden supporters, Biden was also the top second choice of Warren supporters. Morning Consult’s results also strongly disagreed with the Civiqs poll — according to Morning Consult, Biden was also the top second choice of Sanders supporters. One thing to keep in mind, though, is that Morning Consult has consistently shown good numbers for Biden (better than many other pollsters), which could help explain why Biden is such a popular second-choice pick here.

Finally, in a Fox News poll conducted just last week (Oct. 6-8), Biden was the first choice of 32 percent of respondents, Warren 22 percent, Sanders 17 percent, Harris 5 percent and Buttigieg 4 percent. Although it too was a good poll for Biden overall, its second-choice data was more similar to that of the Civiqs and NBC/Wall Street Journal polls. Among Warren supporters, Sanders was the top second choice with 24 percent, followed by Biden at 17 percent; Harris and Buttigieg were tied with 16 percent. And among Biden supporters, Warren (30 percent) and Sanders (26 percent) were both popular second choices; Harris (11 percent) and Buttigieg (9 percent) were further back.

Despite the polls’ occasional disagreements, I still think there are a few conclusions we can draw from this data: