Who stands to gain if DeSantis drops out? Or Haley? Or Christie?

When North Dakota Gov. Doug Burgum dropped out of the presidential race, he had so little support that it didn't affect the Republican primary campaign. When former Vice President Mike Pence ended his campaign, the polls didn't really shift. When former Rep. Will Hurd withdrew, it barely made a ripple.

But now, on the verge of the first primaries and caucuses, most candidates left in the race are big fish, and their inevitable (there can be only one nominee, after all) withdrawals have the potential to significantly alter the trajectory of the campaign. If Florida Gov. Ron DeSantis finished third in Iowa and decided to end his campaign, a not-insignificant 12 percent of Republican voters nationwide* would be up for grabs. If former New Jersey Gov. Chris Christie bowed out before New Hampshire, 11 percent of Granite State Republicans would be looking for a new candidate. Whom would they turn to?

To find out, we aggregated all the national, Iowa and New Hampshire polls we could find from the past two months that asked Republican voters who their second choice for president is.** And it turns out that people's answers greatly depended on who they said their first choice for president was. In other words, there are relatively well-defined lanes in the 2024 Republican primary.

According to the "lanes" theory of presidential primaries, instead of competing over a homogenous voting pool with every other candidate in the field, candidates are really running in mini-primaries against their most like-minded opponents for specific coalitions within the party. (For example, candidates running in the "moderate lane" are mostly fighting with each other for the support of moderate voters rather than trying to win over the hearts and minds of conservative voters from conservative candidates.)

This way of thinking about primaries can be overly simplistic — neither candidates nor voters fit into such neat boxes, and if a candidate in a certain lane drops out, 100 percent of their support does not automatically go to the other candidates in their lane. But empirically, rough lanes do exist in primaries, and they dictate where the bulk of a candidate's support goes when they drop out. And here in 2024, there is one lane in the Republican primary for candidates and voters who support the direction former President Donald Trump has taken the party, and another for those who oppose it.

Just look at businessman Vivek Ramaswamy. Now, it's difficult to know the exact breakdown of Ramaswamy supporters' second choices because the sample size of Ramaswamy supporters is so small in most polls (he's averaging just 5 percent nationally, which means a 500-person poll would have only about 25 Ramaswamy supporters), and small sample sizes yield results with very high margins of error. But we can be more confident in those small crosstabs when we aggregate them and find that they all say roughly the same thing, which is the case here: If Ramaswamy weren't in the race, most of his voters would be supporting Trump.

Compare that to second-choice polls of Christie's supporters, which suffer from the same problem of small sample size but likewise paint a consistent picture. In every poll we collected, a plurality or majority of Christie supporters said they would support former U.N. Ambassador Nikki Haley if Christie were not in the race. Very few said they would support Trump, Ramaswamy or DeSantis.

The reason for this isn't hard to figure out: Christie has made his entire campaign about the dangers of reelecting Trump. Trump and the two candidates who most closely echo his style and rhetoric are unlikely to appeal to the sort of Republicans drawn to that message. Instead, they favor the other top candidate in the race who has criticized Trumpism*** and who hails from the old guard of the Republican Party. As 538 wrote the other day, this is a frustration for Haley in New Hampshire in particular, where she is "just" 13 percentage points behind Trump in the polls. If Christie dropped out and half of his 11 percent support in New Hampshire went to Haley, as suggested by these numbers, it would significantly cut into her deficit. (No, it wouldn't be enough to erase Trump's lead, but if Haley continues to rise in New Hampshire — say, if she gets a boost after a strong performance in Iowa — it could be decisive.)

Meanwhile, DeSantis seems to have one foot in each lane. Nationally, most of his supporters said their second choice was Trump, but a significant minority in each poll said it was Haley. But in polls of Iowa, it's the reverse: A plurality of DeSantis's supporters said that Haley was their second choice, while a big chunk still said Trump was.

This is probably simply because different voters have different reasons for supporting DeSantis. Some might like the strongly conservative stance he has taken on social issues as governor of Florida; in DeSantis's absence, those voters might default to his fellow culture warrior Trump. But some DeSantis supporters are undoubtedly supporting him because they want to move on from Trump, and it makes sense that their second choice is Haley.

Frustratingly, it's not clear who DeSantis supporters in New Hampshire would flock to if DeSantis were to drop out after Iowa. According to the most recent Emerson College/WHDH-TV poll, it would be Haley — but according to a University of New Hampshire/CNN poll taken around the same time, it would be Trump. And both polls are almost two months out at this point, so really we're flying blind.

Considering that she is currently polling better than she ever has, Haley's withdrawal from the race feels further away than Christie's, Ramaswamy's or DeSantis's, but let's take a look at her supporters' second choices as well. Unsurprisingly, their top alternative is either Christie or DeSantis, depending on the poll. Relatively few Haley supporters would switch to Trump.

Finally, let's entertain the very unlikely scenario in which Trump drops out. Obviously, it would throw the primary into chaos to have more than half of voters suddenly up for grabs, but the candidate best positioned to benefit seems like it would be DeSantis. On average, 43 percent of Trump supporters nationally identified him as their second choice.

That said, in Iowa and New Hampshire, Trump's supporters would split roughly evenly between DeSantis and Ramaswamy, raising the possibility that Ramaswamy could score an early-state win that might propel his campaign forward nationally. And a not-insignificant share of Trump supporters opt for Haley as their second choice, so she wouldn't be doomed in this scenario either.

All that said, take these numbers with a grain of salt. Second-choice polling often isn't as helpful as we want it to be: Voters' second choices are subject to a lot of change over the course of a campaign — even more than their first choices — and can be swayed by things like the candidate endorsing someone else on their way out of the race. And again, for all the candidates above except Trump, the sample sizes on these crosstabs are so small that they have very wide margins of error.

I recommend taking generalities away from this article ("Ramaswamy's voters will mostly flow to Trump") rather than specifics ("43 percent of DeSantis's voters in Iowa would go to Haley if he drops out"). But those generalities can still be useful for predicting where the primary will go next if a candidate drops out — and over the next couple months, that will probably happen multiple times.

Cooper Burton contributed research.

Footnotes

*All numbers in this article are as of 10 a.m. Eastern.

**If a pollster conducted multiple second-choice polls in the past two months, we looked at only the most recent one, except in the case of YouGov/The Economist, which was kind enough to aggregate its two most recent surveys together in order to give us a larger sample size. We used only second-choice polls that released or shared with us full crosstabs by first-choice candidate.

***DeSantis has criticized Trump personally but hasn't really objected to the populist direction he has taken the Republican Party. And while former Arkansas Gov. Asa Hutchinson has criticized Trumpism, he has been a nonfactor in the race.